Viessmann Vitodens 222-F B2TF Fault codes & diagnostics

185 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 2020-present
Download the Viessmann Vitodens 222-F B2TF manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
8 Emergency 128 High 18 Medium 31 Low
Just want the most common Viessmann Vitodens 222-F B2TF faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 185 documented codes

Tap any card for details

A.11

Your boiler’s water pressure has dropped too low for it to operate safely, causing the system to shut down.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver braided hose with two small valves) underneath the boiler.
  2. Open both valves slowly until you hear water entering the system.
  3. Watch the pressure gauge on the boiler screen and close both valves firmly when it reaches 1.5 bar.

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for A.11
A.12

Your boiler's internal clock has lost power because its small backup battery has run out, which might affect your timed heating schedules.

Low DIY-safe £5-15

What to check first

  1. Locate the control unit on the front of the boiler
  2. Open the control unit housing to access the Heat Management Unit (HMU) circuit board
  3. Carefully remove the depleted CR2032 coin cell battery and replace it with a new one
  4. Reassemble the unit and reset the time and date on the display

Parts commonly replaced

  • CR2032 Lithium Battery

Related codes

Full explanation for A.12
A.18

Water is getting backed up inside the main burner area of your boiler because it cannot drain away properly.

High Engineer only £120-280

Parts commonly replaced

  • Condensate Trap
  • Flexible Condensate Pipework
  • Ionisation Electrode

Related codes

Full explanation for A.18
A.19

Your boiler has detected that it has become too hot and has automatically shut down to prevent any damage or safety hazards.

High Engineer only £150-300

Parts commonly replaced

  • High limit thermostat
  • Primary flow sensor
  • Circulation pump

Related codes

Full explanation for A.19
A.20

Your boiler is reminding you that it is due for its annual maintenance check, but the system has encountered a small software glitch while trying to register this update.

Low Engineer only £100-180

Related codes

Full explanation for A.20
F.5

Your boiler has stopped working because it cannot accurately measure the temperature of the water flowing through the system due to a sensor fault.

High Engineer only £120-£200

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Wiring harness
  • Control PCB

Related codes

Full explanation for F.5
F.7

Your boiler is unable to read the temperature of the internal storage tank, which means it cannot heat your hot water correctly.

High Engineer only £140-230

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for F.7
F.8

Your boiler has lost its connection to the sensor that monitors your hot water storage, meaning it cannot safely heat your water.

High Engineer only £140-£260

Parts commonly replaced

  • Cylinder temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for F.8
F.11

Your boiler has lost connection with the sensor that monitors the solar heating panels on your roof, meaning it cannot accurately track the temperature up there.

Low Engineer only £120-£250

Parts commonly replaced

  • Collector temperature sensor (NTC)
  • Solar control cable

Related codes

Full explanation for F.11
F.12

Your boiler has detected a technical fault with the sensor that monitors your solar heating system, which may prevent it from heating water efficiently.

Low Engineer only £120-£200

Parts commonly replaced

  • Collector temperature sensor (NTC)
  • Sensor wiring harness
  • Solar control module

Related codes

Full explanation for F.12
Showing 11–20 of 185
F.13

Your boiler has lost its connection to the sensor that measures the temperature outdoors, which may cause your heating to behave unpredictably.

Low Engineer only £90-180

Parts commonly replaced

  • Outside temperature sensor
  • Wiring loom/sensor cable

Related codes

Full explanation for F.13
F.14

Your boiler is struggling to understand the weather outside because the external thermometer has developed an electrical fault.

Medium Engineer only £120-210

Parts commonly replaced

  • Outside temperature sensor (NTC)
  • External sensor wiring
  • Control PCB

Related codes

Full explanation for F.14
F.15

Your boiler has lost connection with the sensor that monitors the temperature of your solar hot water cylinder, meaning it cannot accurately manage water heating from that source.

Low Engineer only £120-£200

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for F.15
F.16

Your boiler has detected an electrical connection problem with the sensor that monitors your solar hot water cylinder temperature.

Low Engineer only £90-180

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor wiring harness
  • EM-S1 Solar module

Related codes

Full explanation for F.16
F.19

Your boiler has lost the connection to the temperature sensor inside your hot water tank, so it currently does not know when your water is hot enough and has stopped heating it.

High Engineer only £150-250

Parts commonly replaced

  • DHW cylinder temperature sensor
  • Wiring harness

Related codes

Full explanation for F.19
F.29

Your boiler has lost communication with a sensor that monitors water temperature, which may cause your heating to stop working correctly.

Medium Engineer only £120-220

Parts commonly replaced

  • Low loss header temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for F.29
F.30

A sensor that monitors water temperature for your heating system has developed an electrical fault and is preventing the boiler from working correctly.

High Engineer only £120-220

Parts commonly replaced

  • Low loss header temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for F.30
F.49

Your boiler has detected a broken connection or a fault with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.

High Engineer only £140-£220

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

Full explanation for F.49
F.50

The boiler has detected a faulty internal sensor that monitors exhaust gases, causing the system to shut down for safety.

High Engineer only £140-£220

Parts commonly replaced

  • Flue gas temperature sensor (NTC)
  • Wiring harness

Related codes

Full explanation for F.50
F.57

Your boiler has lost its connection to the indoor thermostat or temperature sensor, meaning it doesn't know how warm your house is.

Medium DIY-safe £90-220

What to check first

  1. Check if your wireless thermostat has run out of batteries and replace them if necessary
  2. Ensure the thermostat or room sensor is within range of the boiler and hasn't been moved
  3. Check for any loose visible wires if your thermostat is the plug-in type

Parts commonly replaced

  • Room temperature sensor
  • Thermostat batteries
  • Connecting cable/wiring loom

Related codes

Full explanation for F.57
Showing 21–30 of 185
F.58

Your boiler has lost communication with the internal sensor that monitors the temperature inside your home, meaning it doesn't know when to turn the heating on or off.

Medium Engineer only £120-£240

Parts commonly replaced

  • Room temperature sensor
  • NTC thermistor
  • Wiring harness

Related codes

Full explanation for F.58
F.59

Your boiler has detected an electrical power issue or a drop in voltage, causing it to shut down for safety.

High DIY-safe £120-450

What to check first

  1. Check if there are any signs of a power cut or if other appliances in the home are struggling.
  2. Locate your boiler's power switch or fuse spur and turn it off for 30 seconds, then turn it back on.
  3. Press the 'Reset' button on the boiler control panel once power is stable.

Parts commonly replaced

  • External Voltage Stabiliser
  • Power Supply Unit (PSU)
  • Electronic Control PCB

Related codes

Full explanation for F.59
F.62

Your boiler has automatically shut down because it detected it is getting too hot, preventing internal damage or safety issues.

High Engineer only £150-450

Parts commonly replaced

  • System Pump
  • High Limit Thermostat
  • Heat Exchanger cleaning
  • Diverter Valve

Related codes

Full explanation for F.62
F.63

Your boiler has shut down because it detected that the exhaust gases have become dangerously hot, which acts as a safety measure to prevent damage to the flue system.

Emergency Engineer only £150-450

Parts commonly replaced

  • Flue gas temperature sensor
  • Heat exchanger (cleaning or replacement)
  • Burner gasket

Related codes

Full explanation for F.63
F.64

Your boiler is struggling to keep the flame lit while it is starting up, so it is automatically turning itself off and trying again to get back to normal.

Medium Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Ionisation probe
  • Gas valve

Related codes

Full explanation for F.64
F.65

Your boiler is failing to ignite because it cannot detect a flame, meaning your heating and hot water will not work until a professional inspects the internal ignition components.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Ionisation electrode
  • Gas valve
  • Control board

Related codes

Full explanation for F.65
F.67

Your boiler has stopped working because it cannot properly detect the flame needed to heat your water and radiators.

High Engineer only £140-£320

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Burner control unit

Related codes

Full explanation for F.67
F.68

Your boiler has detected a flame before it has even tried to light, which is a safety conflict that prevents it from starting up.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Burner control unit (PCB)

Related codes

Full explanation for F.68
F.69

Your boiler is struggling to detect a stable flame during its self-calibration process and has locked out for safety.

High Engineer only £180-450

Parts commonly replaced

  • Ionisation electrode
  • Ignition cable
  • Gas valve
  • PCB

Related codes

Full explanation for F.69
F.70

Your boiler's computer has detected an internal electronic error and has stopped working to ensure safety.

High Engineer only £350-£650

Parts commonly replaced

  • HMU Heat Management Unit
  • BCU Burner Control Unit
  • Wiring Harness

Related codes

Full explanation for F.70
Showing 31–40 of 185
F.71

Your boiler has stopped working because the fan that clears exhaust gases is not spinning fast enough to operate safely.

High Engineer only £250-£550

Parts commonly replaced

  • Fan assembly
  • Control PCB
  • Wiring harness

Related codes

Full explanation for F.71
F.72

Your boiler's fan is still spinning when it should be stopped, which prevents the system from starting safely.

High Engineer only £200-£450

Parts commonly replaced

  • Extraction fan
  • HMI control unit
  • Wiring harness

Related codes

Full explanation for F.72
F.73

Your boiler's internal computer parts are struggling to talk to each other, which means the system has shut down as a safety precaution.

High DIY-safe £150-450

What to check first

  1. Locate the power switch for the boiler and turn it off for 30 seconds
  2. Turn the power back on and wait for the system to reboot
  3. If the code persists, press the Reset button on the control panel once

Parts commonly replaced

  • Communication cable/harness
  • Electronic control unit (PCB)
  • HMI touch display unit

Related codes

Full explanation for F.73
F.74

Your boiler has detected that the water pressure is too low to operate safely, so it has shut itself down to prevent damage.

High DIY-safe £0-120

What to check first

  1. Locate the internal or external filling loop (usually two braided hoses or blue levers under the boiler).
  2. Slowly open the valves to let water into the system while watching the pressure gauge.
  3. Close the valves firmly once the pressure reaches between 1.0 and 1.5 bar.
  4. Press the 'Reset' button on the boiler control panel to clear the fault.

Parts commonly replaced

  • External filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F.74
F.75

Your boiler has stopped working because it cannot detect any water moving through the system to heat up your home.

High Engineer only £200-450

Parts commonly replaced

  • Circulation pump
  • Pressure sensor

Related codes

Full explanation for F.75
F.77

Your boiler's internal computer is having difficulty reading or storing its settings, which has caused the system to stop working for safety.

High Engineer only £250-£550

Parts commonly replaced

  • Burner Control Unit
  • EVCU (Electronic Control Unit)
  • HMI HMU Module

Related codes

Full explanation for F.77
F.78

Your boiler's main control panel is struggling to communicate with the internal system, which is preventing the boiler from functioning correctly.

High Engineer only £150-350

Parts commonly replaced

  • Communication cable
  • Control unit (HMU)
  • Programming unit interface

Related codes

Full explanation for F.78
F.80

Your boiler has detected an electrical fault with one of its internal sensors, which is currently preventing the system from operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • ADIO module
  • Sensor wiring harness
  • Temperature sensor

Related codes

Full explanation for F.80
F.87

Your boiler has stopped working because the water pressure inside the heating system is currently too high.

Medium DIY-safe £80-150

What to check first

  1. Locate a radiator with a bleed valve and place a cloth underneath
  2. Open the valve slightly using a radiator key to let water out until the pressure gauge on the boiler drops into the green zone (usually 1.0 to 1.5 bar)
  3. Close the valve and check the boiler display to see if the error code clears

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F.87
F.89

Your boiler's internal pump has stopped moving water around the system, which means your heating and hot water will not work until it is cleared or replaced.

High Engineer only £280-550

Parts commonly replaced

  • Internal circulation pump
  • Pump motor head
  • Expansion vessel (if damaged by pressure)

Related codes

Full explanation for F.89
Showing 41–50 of 185
F.91

Your boiler's internal computer is having trouble communicating with one of its control modules, which is preventing the system from operating correctly.

High Engineer only £180-450

Parts commonly replaced

  • DIO Electronics Module
  • Communication Cable Harness
  • Main PCB

Related codes

Full explanation for F.91
F.92

Your boiler's internal control computer has lost contact with one of its main electronic modules, meaning the system cannot communicate internally to manage heating and hot water.

High Engineer only £180-450

Parts commonly replaced

  • ADIO Electronics Module
  • Internal Wiring Harness
  • Main PCB

Related codes

Full explanation for F.92
F.93

Your boiler is having trouble 'talking' to an internal control unit, which means it may not be able to manage your heating zones or hot water correctly while in emergency mode.

Medium Engineer only £180-350

Parts commonly replaced

  • M2IO extension module
  • Communication cable/wiring harness
  • Main PCB

Related codes

Full explanation for F.93
F.94

Your boiler's internal computer system has lost communication between its internal control boards, meaning it cannot process instructions to provide heating or hot water.

High Engineer only £250-£650

Parts commonly replaced

  • SDIO Electronics Module
  • HMU (Heat Management Unit) Board
  • Internal wiring harness

Related codes

Full explanation for F.94
F.100

Your boiler has stopped working because of a communication problem between its electronic brains and the internal control system.

High Engineer only £180-450

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • Communication Module
  • PlusBus Wiring Harness

Related codes

Full explanation for F.100
F.104

Your boiler has received an 'alert' signal from an external part of your heating system, such as a smart thermostat or a safety accessory, which has told the boiler to stop running.

High DIY-safe £70-180

What to check first

  1. Check your thermostat or smart home app for any error messages or low battery warnings.
  2. Ensure any external pumps or safety switches attached to the system are powered on.
  3. Restart the boiler by pressing the reset button to see if the external signal clears.

Parts commonly replaced

  • External thermostat
  • Wiring harness
  • Condensate pump

Related codes

Full explanation for F.104
F.142

Your boiler has stopped working because the internal computer cannot talk to the fan that manages the gas burner.

High Engineer only £280-£550

Parts commonly replaced

  • Fan motor unit
  • CAN bus wiring harness
  • Electronic Control Unit (PCB)

Related codes

Full explanation for F.142
F.160

Your boiler's internal computer brains are having trouble talking to each other, which has caused the system to stop working for safety.

High Engineer only £180-450

Parts commonly replaced

  • Wiring harness
  • Electronic controller (HMU)
  • Burner Control Unit

Related codes

Full explanation for F.160
F.161

Your boiler's computer memory has encountered an internal reading error, preventing it from functioning correctly.

High Engineer only £250-£650

Parts commonly replaced

  • Electronic Control Unit (BCU)
  • Main PCB

Related codes

Full explanation for F.161
F.162

Your boiler has detected an electrical inconsistency in its internal control system and has safely shut down to prevent potential damage.

High Engineer only £150-350

Parts commonly replaced

  • Control Unit
  • Main PCB
  • Wiring Harness

Related codes

Full explanation for F.162
Showing 51–60 of 185
F.163

Your boiler's internal computer is having difficulty reading its own saved settings, which has caused the system to stop working for safety.

High Engineer only £350-£650

Parts commonly replaced

  • Burner Control Unit (BCU)
  • Electronic Control PCB

Related codes

Full explanation for F.163
F.180

Your boiler has stopped working because it is not receiving the correct amount of gas, meaning it cannot safely light to provide you with heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Gas regulator
  • Gas supply pipework

Related codes

Full explanation for F.180
F.182

Your boiler has detected a technical fault with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely manage your heating or hot water.

High Engineer only £120-£200

Parts commonly replaced

  • Outlet temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for F.182
F.183

Your boiler has lost its connection to the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.

High Engineer only £120-210

Parts commonly replaced

  • Outlet temperature sensor (NTC)
  • Wiring harness connector

Related codes

Full explanation for F.183
F.184

Your boiler has identified an electrical fault with its temperature monitoring system and has shut down as a safety precaution to prevent overheating.

High Engineer only £140-£260

Parts commonly replaced

  • Flow temperature sensor
  • High limit safety cut-out
  • Wiring harness

Related codes

Full explanation for F.184
F.185

Your boiler has detected a signal failure from an internal safety sensor, causing the system to shut down to prevent overheating.

High Engineer only £140-£260

Parts commonly replaced

  • Flow temperature sensor
  • High limit safety cut-out
  • Wiring harness

Related codes

Full explanation for F.185
F.299

Your boiler's internal clock has lost its settings, which can happen after a power cut or a long period of being switched off.

Low DIY-safe £0-80

What to check first

  1. Navigate to the main menu on the boiler control panel
  2. Select 'Settings'
  3. Choose 'Time and Date' and update to the current local time
  4. Confirm the settings to clear the fault code

Parts commonly replaced

  • None (Software adjustment only)
  • HMI Control Unit (Rare cases)

Related codes

Full explanation for F.299
F.342

Your boiler's internal control computer has lost its connection with the burner, meaning the system cannot safely light the flame to provide heat or hot water.

High Engineer only £250-£550

Parts commonly replaced

  • Burner Control Unit (BCU)
  • Wiring Harness
  • Electronic Control Board

Related codes

Full explanation for F.342
F.345

Your boiler has switched itself off for safety because it detected that the water inside has become far too hot.

High Engineer only £120-350

Parts commonly replaced

  • High Limit Thermostat
  • Circulation Pump
  • Main Heat Exchanger

Related codes

Full explanation for F.345
F.346

Your boiler is having trouble measuring and adjusting its own flame, which prevents it from firing up safely.

High Engineer only £140-£320

Parts commonly replaced

  • Ionisation electrode
  • Ignition leads
  • Gas valve
  • Burner control unit

Related codes

Full explanation for F.346
Showing 61–70 of 185
F.348

Your boiler has stopped working because the internal gas valve cannot precisely control the fuel flow needed for the burner.

High Engineer only £250-£450

Parts commonly replaced

  • Gas modulation valve
  • Electronic control unit (PCB)
  • Gas valve wiring harness

Related codes

Full explanation for F.348
F.349

Your boiler is struggling to measure the amount of air it needs to burn gas safely, which has caused the system to stop working for safety reasons.

High Engineer only £180-450

Parts commonly replaced

  • Fan assembly
  • Air mass sensor
  • Wiring harness

Related codes

Full explanation for F.349
F.350

Your boiler has detected a problem with the flame that is used to heat your water, causing the system to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Burner gasket
  • Gas valve

Related codes

Full explanation for F.350
F.351

Your boiler is struggling to detect a stable flame, causing it to shut down for safety purposes.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Burner gasket

Related codes

Full explanation for F.351
F.352

Your boiler has detected dangerously high levels of carbon monoxide and has shut down as a safety precaution.

Emergency Engineer only £150-450

Parts commonly replaced

  • Gas valve
  • Burner gasket
  • Flue system components
  • Ignition electrode

Related codes

Full explanation for F.352
F.353

Your boiler is not receiving enough gas to run at full power, so it has automatically lowered its performance to stay operational.

Medium DIY-safe £100-350

What to check first

  1. Check that your external gas meter has credit (if on a prepayment meter)
  2. Ensure your main gas emergency control valve is fully open
  3. Check if other gas appliances, like a hob, have a strong flame to rule out a wider grid issue

Parts commonly replaced

  • Gas Valve
  • Gas Pressure Regulator
  • Burner Gasket

Related codes

Full explanation for F.353
F.354

Your boiler has detected a problem with the part that controls the gas supply, meaning it cannot safely adjust the flame to the correct size.

High Engineer only £180-450

Parts commonly replaced

  • Gas Valve
  • Burner Control Unit
  • Ignition Electrodes

Related codes

Full explanation for F.354
F.355

Your boiler is detecting a flame when there shouldn't be one, which means the safety system has stopped the boiler from starting up for your protection.

High Engineer only £180-450

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Burner control unit (PCB)

Related codes

Full explanation for F.355
F.357

Your boiler is struggling to get enough gas to stay lit, which means it cannot provide heating or hot water until the supply is restored.

High DIY-safe £120-350

What to check first

  1. Check that your gas meter has credit (if using a pre-payment meter).
  2. Ensure the gas emergency control valve (usually located by the meter) is in the 'on' position.
  3. Check if other gas appliances, like a hob, are working to confirm a house-wide supply issue.
  4. If you have an external gas meter and it is freezing weather, the regulator may be frozen; contact your gas supplier.

Parts commonly replaced

  • Gas valve
  • Gas pressure regulator
  • Ignition electrodes

Related codes

Full explanation for F.357
F.359

Your boiler is failing to create the spark needed to light the gas burner, meaning your heating and hot water will not work.

High Engineer only £120-£280

Parts commonly replaced

  • Ignition electrode
  • Ignition lead
  • Ignition transformer
  • PCB

Related codes

Full explanation for F.359
Showing 71–80 of 185
F.361

Your boiler is trying to light, but it cannot detect a flame, which means your heating and hot water will not work.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure your gas supply is active
  2. If you have a pre-payment meter, check that you have remaining credit
  3. Press the 'Reset' button on the boiler control panel once to see if it restarts

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Ignition transformer

Related codes

Full explanation for F.361
F.365

Your boiler has detected a safety concern where the gas supply system is not switching off correctly, so it has shut down to prevent potential danger.

Emergency Engineer only £200-400

Parts commonly replaced

  • Gas valve
  • Boiler control unit (PCB)

Related codes

Full explanation for F.365
F.366

Your boiler has detected a safety issue with the gas control valve, meaning it cannot properly shut off the fuel supply, and it has locked out to keep your home safe.

Emergency Engineer only £250-£550

Parts commonly replaced

  • Gas valve
  • Boiler control unit (PCB)
  • Wiring harness

Related codes

Full explanation for F.366
F.367

Your boiler has detected an internal electrical safety issue where the gas supply valve is not closing correctly, causing the system to shut down for your protection.

High Engineer only £250-£550

Parts commonly replaced

  • Gas valve
  • Electronic control PCB
  • Wiring harness

Related codes

Full explanation for F.367
F.368

Your boiler has detected an issue with its internal air or gas flow, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £150-350

Parts commonly replaced

  • Gas pressure switch
  • Fan assembly
  • Air pressure switch
  • PCB

Related codes

Full explanation for F.368
F.369

Your boiler is managing to light a flame, but it goes out immediately because the system cannot confirm it is burning safely.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Burner gasket

Related codes

Full explanation for F.369
F.370

Your boiler has detected a safety issue where the gas supply is failing to shut off properly, causing the system to lock out for your protection.

Emergency Engineer only £250-£450

Parts commonly replaced

  • Gas valve
  • Burner control unit (PCB)

Related codes

Full explanation for F.370
F.371

Your boiler has stopped working because the internal fan that clears exhaust gases isn't spinning fast enough, so the system has shut down to stay safe.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F.371
F.372

Your boiler is struggling to keep its flame lit while trying to automatically adjust its settings for efficient burning.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Flue system seals

Related codes

Full explanation for F.372
F.373

Your boiler is struggling to circulate enough heat through the system to complete its internal safety checks.

High DIY-safe £120-350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the display
  2. Ensure at least two or three radiators have their valves fully open
  3. Check that the magnetic system filter is not blocked
  4. Restart the boiler to allow it to attempt a new calibration

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor
  • Plate heat exchanger

Related codes

Full explanation for F.373
Showing 81–90 of 185
F.375

Your boiler has detected an issue with the system that lights the flame, meaning it cannot safely start up to provide heating or hot water.

High Engineer only £150-350

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Boiler control unit (PCB)

Related codes

Full explanation for F.375
F.377

The boiler is struggling to automatically adjust its internal burner settings during a routine check, often due to an unstable gas supply or a worn ignition component.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition cable
  • Gas valve
  • FLUE system seals

Related codes

Full explanation for F.377
F.378

Your boiler is struggling to keep its flame lit properly, which is causing the system to shut down for safety.

High Engineer only £150-450

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Burner gasket

Related codes

Full explanation for F.378
F.379

Your boiler is failing to light the gas or cannot detect that it has successfully stayed lit, resulting in the system shutting down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Condensate trap

Related codes

Full explanation for F.379
F.380

Your boiler is struggling to keep its flame lit, which is causing the system to shut down for safety purposes.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Condensate trap

Related codes

Full explanation for F.380
F.381

Your boiler started to heat up but the flame unexpectedly went out, causing the system to shut down for safety.

High Engineer only £140-£380

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Condensate trap

Related codes

Full explanation for F.381
F.382

Your boiler has stopped working because it has tried and failed to restart itself too many times due to an underlying ignition or sensing problem.

High Engineer only £120-350

Parts commonly replaced

  • Ignition electrode
  • Flame rectification lead
  • Gas valve
  • Burner gasket

Related codes

Full explanation for F.382
F.383

Your boiler has detected that the gas supply might be blocked or contaminated, which is preventing the burner from lighting safely.

High Engineer only £120-350

Parts commonly replaced

  • Gas valve
  • Burner gasket
  • Gas filter

Related codes

Full explanation for F.383
F.384

Your boiler has detected a potential issue with the gas supply being blocked or contaminated, which prevents it from firing safely.

High Engineer only £120-350

Parts commonly replaced

  • Gas valve
  • Flame ionisation electrode
  • Gas filter

Related codes

Full explanation for F.384
F.385

Your boiler has detected an electrical fault with the flame sensing system or its internal control board, preventing it from heating your home safely.

High Engineer only £180-£550

Parts commonly replaced

  • Ionisation electrode
  • Burner Control Unit (BCU)
  • Wiring harness

Related codes

Full explanation for F.385
Showing 91–100 of 185
F.386

Your boiler's electronic control brain has developed a critical internal failure and can no longer safely manage the burner.

High Engineer only £350-£650

Parts commonly replaced

  • BCU Burner Control Unit
  • Main PCB
  • Wiring Harness

Related codes

Full explanation for F.386
F.387

Your boiler has detected an electrical fault within its internal control system that prevents it from managing the flame safely.

High Engineer only £450-£700

Parts commonly replaced

  • Burner Control Unit (BCU)
  • Main PCB
  • Ionisation Electrode

Related codes

Full explanation for F.387
F.388

Your boiler's main internal computer has developed a serious fault and is unable to control the burner safely, causing the system to shut down.

High Engineer only £450-£700

Parts commonly replaced

  • BCU Burner Control Unit
  • HMI Controller Board
  • Wiring Harness

Related codes

Full explanation for F.388
F.394

Your boiler has detected a disconnection in a safety sensor that monitors the exhaust temperatures, causing it to shut down to prevent unsafe operation.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

Full explanation for F.394
F.395

Your boiler has detected an internal electrical fault with its ignition sensor system, meaning it cannot safely confirm if the gas has lit correctly.

High Engineer only £250-£650

Parts commonly replaced

  • Ionisation electrode
  • Burner Control Unit (BCU)
  • Wiring harness

Related codes

Full explanation for F.395
F.396

Your boiler's computerised control brain has developed a critical internal error and can no longer safely operate the burner.

High Engineer only £350-£600

Parts commonly replaced

  • BCU Burner Control Unit
  • HMI Controller

Related codes

Full explanation for F.396
F.399

Your boiler has detected an internal electrical problem with its ignition system or its main control board, preventing it from firing up safely.

High Engineer only £250-£650

Parts commonly replaced

  • Ionisation Electrode
  • Burner Control Unit (BCU)
  • Wiring Harness

Related codes

Full explanation for F.399
F.400

Your boiler's main internal computer has developed a serious electronic failure and can no longer control the burner safely.

High Engineer only £450-£700

Parts commonly replaced

  • BCU Burner Control Unit
  • Electronic PCB

Related codes

Full explanation for F.400
F.401

Your boiler has detected an electrical grounding issue with its internal ignition components or a fault in the central control unit, which prevents it from starting safely.

High Engineer only £180-£650

Parts commonly replaced

  • Ionisation Electrode
  • Burner Control Unit (BCU)
  • Wiring Harness

Related codes

Full explanation for F.401
F.402

Your boiler's main internal computer has developed a serious electronic fault and can no longer safely control the burner, meaning your heating and hot water will not work.

High Engineer only £450-£700

Parts commonly replaced

  • BCU Burner Control Unit
  • HMI Operator Unit
  • Main PCB

Related codes

Full explanation for F.402
Showing 101–110 of 185
F.403

Your boiler has detected an electrical issue with the flame sensing component or its main control unit, preventing the system from firing up safely.

High Engineer only £180-450

Parts commonly replaced

  • Ionisation electrode
  • Burner Control Unit (BCU)
  • Wiring harness

Related codes

Full explanation for F.403
F.404

Your boiler's computer brain has encountered an internal electronic failure and cannot safely control the burner, causing the system to shut down.

High Engineer only £350-£600

Parts commonly replaced

  • BCU Burner Control Unit
  • HMI (Display) Module
  • Main PCB

Related codes

Full explanation for F.404
F.405

Your boiler has detected an internal electrical fault with its ignition and safety monitoring components, preventing it from firing up safely.

High Engineer only £250-£550

Parts commonly replaced

  • Ionisation electrode
  • Burner Control Unit (BCU)
  • Wiring harness

Related codes

Full explanation for F.405
F.406

Your boiler's main internal computer has developed a serious electronic fault, preventing the burner from firing safely.

High Engineer only £350-£650

Parts commonly replaced

  • BCU Control Unit
  • Main PCB
  • Wiring Harness

Related codes

Full explanation for F.406
F.408

Your boiler's main internal computer has developed a serious electronic fault and can no longer safely control the burner, meaning your heating and hot water will not work.

High Engineer only £450-£700

Parts commonly replaced

  • BCU Burner Control Unit
  • HMI Controller
  • Main Circuit Board (PCB)

Related codes

Full explanation for F.408
F.410

Your boiler's internal computer has suffered a critical failure and can no longer safely control the burner, meaning the system will not provide any heat or hot water.

High Engineer only £350-550

Parts commonly replaced

  • BCU (Burner Control Unit)
  • Control PCB

Related codes

Full explanation for F.410
F.416

Your boiler has shut down because it thinks a safety sensor for exhaust gases is not in the correct position.

High Engineer only £120-£250

Parts commonly replaced

  • Flue gas temperature sensor
  • Sensor mounting clip

Related codes

Full explanation for F.416
F.417

Your boiler's main control computer has developed an internal electrical fault and can no longer safely operate the burner.

High Engineer only £350-£650

Parts commonly replaced

  • BCU Burner Control Unit
  • Electronic PCB

Related codes

Full explanation for F.417
F.418

Your boiler's internal computer has developed a serious communication or hardware failure and can no longer safely control the burner.

High Engineer only £350-£650

Parts commonly replaced

  • BCU Burner Control Unit
  • HMI Operator Interface
  • Main PCB

Related codes

Full explanation for F.418
F.425

Your boiler is having trouble connecting to the internet or its external time source, which may affect your heating schedule and efficiency.

Low DIY-safe £0-80

What to check first

  1. Check your home internet connection and Wi-Fi router to ensure they are working.
  2. Restart your internet router and wait 5 minutes.
  3. Reset the boiler using the control panel to prompt a new connection attempt.

Parts commonly replaced

  • None (Communication issue)
  • WiFi Module

Related codes

Full explanation for F.425
Showing 111–120 of 185
F.430

Your boiler has lost its connection to its internal communication module, meaning it cannot properly send or receive control signals.

Medium DIY-safe £120-350

What to check first

  1. Switch the boiler off at the fused spur or main power switch.
  2. Wait for 60 seconds.
  3. Switch the boiler back on and wait for the system to reboot to see if the connection is restored.

Parts commonly replaced

  • Communication module (Gateway)
  • Wiring harness
  • Electronic Control Unit (HMU)

Related codes

Full explanation for F.430
F.431

Your boiler is working fine, but it is failing to communicate with your smart home or external heating control system.

Low Engineer only £120-250

Parts commonly replaced

  • KNX communication module
  • Communication cable

Related codes

Full explanation for F.431
F.436

Your boiler has detected an electrical fault with the sensor that measures the flow of water, which is preventing the system from heating up correctly.

High Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

Full explanation for F.436
F.437

Your boiler has lost its connection to the sensor that measures water flow, meaning it cannot properly manage your heating or hot water.

High Engineer only £180-300

Parts commonly replaced

  • Flow sensor
  • Wiring harness

Related codes

Full explanation for F.437
F.446

Your boiler has detected an unusual temperature difference between internal sensors and has shut down as a safety precaution to prevent overheating.

High Engineer only £140-£280

Parts commonly replaced

  • Flow temperature sensor
  • High limit safety cut-out
  • Wiring harness

Related codes

Full explanation for F.446
F.447

Your boiler is having trouble detecting the flame needed to heat your water, which is causing the system to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for F.447
F.448

Your boiler is struggling to correctly monitor its own flame, which prevents it from firing safely and effectively.

High Engineer only £140-£320

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Burner control unit

Related codes

Full explanation for F.448
F.449

Your boiler's internal computer has encountered a software timing error, meaning it has lost track of its scheduled safety checks and operations.

High DIY-safe £120-350

What to check first

  1. Locate the power switch for the boiler and turn it off.
  2. Wait for approximately 60 seconds.
  3. Turn the power back on and press the 'Reset' button on the display panel to see if the system clears the error.

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • HMI Display module

Related codes

Full explanation for F.449
F.450

Your boiler's internal computer has encountered a software timing error, causing it to lose its place during its normal operating sequence.

High DIY-safe £120-450

What to check first

  1. Press the Reset button on the control panel to clear the temporary software glitch.
  2. Turn the power supply to the boiler off at the fused spur switch, wait 30 seconds, and turn it back on.
  3. Check that the boiler display is not repeatedly cycling or 'freezing' after the restart.

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • HMI Display module

Related codes

Full explanation for F.450
F.451

Your boiler's internal computer has encountered a software timing error, meaning it is having trouble carrying out its programmed instructions correctly.

High DIY-safe £100-280

What to check first

  1. Locate the power button or switch and turn the boiler off
  2. Wait for approximately 30 seconds
  3. Turn the power back on and wait for the system to reboot

Parts commonly replaced

  • Electronic Control Unit (Main PCB)
  • HMI (Control Display Unit)

Related codes

Full explanation for F.451
Showing 121–130 of 185
F.452

Your boiler has detected an internal issue with its safety monitoring system and has automatically shut down to prevent unsafe operation.

High Engineer only £150-350

Parts commonly replaced

  • Control board (PCB)
  • Wiring harness

Related codes

Full explanation for F.452
F.453

Your boiler has detected a communication glitch while trying to start, so it has shut itself down to prevent any unsafe operation.

High Engineer only £150-300

Parts commonly replaced

  • Main control board (PCB)
  • Wiring harness
  • Burner control unit

Related codes

Full explanation for F.453
F.454

Your boiler's computer has detected that its internal software is incompatible, causing it to shut down for safety reasons.

High Engineer only £250-450

Parts commonly replaced

  • Burner Control Unit (BCU)
  • Main Control Board

Related codes

Full explanation for F.454
F.455

Your boiler's internal computer has encountered a software processing error and has temporarily stopped working to protect itself.

High DIY-safe £150-550

What to check first

  1. Locate the power button or reset symbol on the control panel
  2. Press and hold the reset button for at least 3 seconds
  3. Wait up to 5 minutes for the boiler to complete its restart sequence

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • HMI Command Unit

Related codes

Full explanation for F.455
F.456

Your boiler has detected an internal software error while trying to ignite, causing it to shut down for safety to prevent an uncontrolled burner sequence.

High Engineer only £150-350

Parts commonly replaced

  • Control unit
  • Main PCB
  • Wiring harness

Related codes

Full explanation for F.456
F.457

Your boiler has stopped working because the internal fan that moves air and gas is struggling to spin or is stuck.

High Engineer only £250-£550

Parts commonly replaced

  • Combustion Fan
  • Fan Wiring Harness
  • Control PCB

Related codes

Full explanation for F.457
F.458

Your boiler has stopped working because it has detected an error during its attempt to restart, meaning it needs a technician to safely reset the system's internal safety checks.

High Engineer only £120-250

Parts commonly replaced

  • Ionisation electrode
  • Ignition transformer
  • Control unit

Related codes

Full explanation for F.458
F.463

Your boiler is drawing in its own exhausted fumes instead of fresh air, which is preventing it from burning gas safely.

High Engineer only £120-350

Parts commonly replaced

  • Flue seals
  • Flue ducting
  • Air intake gaskets

Related codes

Full explanation for F.463
F.464

Your boiler is struggling to maintain a stable flame during its automatic self-tuning process, causing it to shut down for safety.

High Engineer only £140-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for F.464
F.467

Your boiler is struggling to get enough gas to set itself up correctly, which has caused it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Gas valve
  • Burner gasket
  • Gas supply pipework

Related codes

Full explanation for F.467
Showing 131–140 of 185
F.468

Your boiler has detected an unusual signal from the flame sensor while trying to adjust itself, and it has shut down for safety.

High Engineer only £140-£350

Parts commonly replaced

  • Ionisation electrode
  • Ignition cable
  • Gas valve
  • Control PCB

Related codes

Full explanation for F.468
F.471

Your boiler is unable to read the water pressure because of a wiring fault or a failed sensor, which has caused the system to stop working for safety.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for F.471
F.473

Your boiler's internal control computers have lost the ability to talk to each other, which has caused the system to stop working for safety.

High Engineer only £250-650

Parts commonly replaced

  • HMU Heat Management Unit
  • Wiring Harness
  • Electronic Control PCB

Related codes

Full explanation for F.473
F.474

Your boiler's internal computer has encountered a software glitch or a communication error that is preventing it from following its programmed instructions.

High DIY-safe £120-£550

What to check first

  1. Press and hold the 'Reset' button on the control panel for 3 seconds.
  2. Turn the boiler power off at the fused spur switch, wait 30 seconds, and turn it back on.
  3. Check that the internet connection is stable if you are using the ViCare app.

Parts commonly replaced

  • HMI (Control Unit)
  • Main PCB
  • WiFi Communication Module

Related codes

Full explanation for F.474
F.477

Your boiler's solar water heating system is struggling to balance temperatures correctly, meaning the solar panels aren't effectively warming your water tank right now.

Low Engineer only £150-300

Parts commonly replaced

  • Solar collector temperature sensor
  • Cylinder temperature sensor
  • Solar circulation pump

Related codes

Full explanation for F.477
F.517

Your boiler is having trouble communicating with its external thermostat or remote control, meaning it cannot receive the correct instructions to heat your home.

High Engineer only £120-350

Parts commonly replaced

  • PlusBus Cable
  • Vitotrol Remote Control
  • HMI Controller Interface

Related codes

Full explanation for F.517
F.527

Your boiler's internal computer has lost its correct configuration settings, meaning it no longer knows exactly how to control the heating and hot water components safely.

High Engineer only £120-450

Parts commonly replaced

  • HMU Heat Management Unit
  • Boiler Coding Card
  • Main PCB

Related codes

Full explanation for F.527
F.528

Your boiler's computer system has detected a configuration error and cannot talk to the burner, meaning it has shut down for safety.

High Engineer only £180-450

Parts commonly replaced

  • Burner Control Unit (BCU)
  • HMI Controller Board
  • Coding Chip

Related codes

Full explanation for F.528
F.530

Your boiler has lost communication with the solar heating system sensors, meaning your solar panels won't be helping to heat your water right now.

Low Engineer only £120-220

Parts commonly replaced

  • Solar temperature sensor (PT1000)
  • Solar control cable

Related codes

Full explanation for F.530
F.538

Your boiler has lost communication with the temperature sensor that tracks the return flow from your solar thermal heating system, meaning it can no longer accurately monitor heat coming from your solar panels.

Medium Engineer only £150-250

Parts commonly replaced

  • Solar return temperature sensor
  • Wiring harness
  • SDIO/Solartrol module

Related codes

Full explanation for F.538
Showing 141–150 of 185
F.539

Your boiler has lost the connection to a sensor responsible for tracking the temperature of the water returning to your heating system.

Medium Engineer only £150-250

Parts commonly replaced

  • System return temperature sensor
  • Wiring harness

Related codes

Full explanation for F.539
F.540

Waste water is backing up inside your boiler's heating unit because it cannot drain away properly.

High DIY-safe £90-180

What to check first

  1. Check the white plastic pipe leading from the boiler to the outside drain for signs of freezing or blockages.
  2. If the external pipe is frozen, gently pour warm (not boiling) water over it to melt the ice.
  3. Ensure the internal condensate trap is not visibly blocked by debris or sludge.

Parts commonly replaced

  • Condensate trap
  • Condensate electrode
  • External pipe insulation

Related codes

Full explanation for F.540
F.544

Your boiler has lost communication with the temperature sensor that controls your second heating zone, meaning that specific part of your home may not heat correctly.

Medium Engineer only £120-£210

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Sensor wiring harness
  • Mixer extension module

Related codes

Full explanation for F.544
F.545

A sensor that monitors the temperature for your second heating zone (such as underfloor heating) has developed an electrical fault, causing your boiler to close the mixing valve to prevent overheating.

Medium Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

Full explanation for F.545
F.546

A sensor responsible for measuring the water temperature in your second heating zone is reporting a fault, which may prevent that specific part of your heating system from warming up correctly.

Medium Engineer only £120-£210

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Sensor Wiring Harness
  • Extension Module (Mixer)

Related codes

Full explanation for F.546
F.547

Your boiler is struggling to control the temperature of your third heating circuit because a sensor has developed an electrical fault.

Medium Engineer only £120-220

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Sensor Wiring Harness
  • Extension Module Electronics

Related codes

Full explanation for F.547
F.548

Your boiler has detected an electrical fault in a sensor that helps regulate the temperature for one of your heating zones.

Medium Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

Full explanation for F.548
F.549

Your boiler has detected an electrical fault in a sensor that helps regulate the temperature for one of your heating zones, causing that specific zone to temporarily shut down.

Medium Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

Full explanation for F.549
F.574

Your boiler is working normally, but it cannot detect the room temperature in your main living area to adjust itself automatically.

Low Engineer only £120-220

Parts commonly replaced

  • Room temperature sensor
  • Connecting cable/wiring
  • Control unit interface

Related codes

Full explanation for F.574
F.575

Your boiler is no longer receiving temperature readings from your wall-mounted room controller and has defaulted to running based on internal settings instead.

Low Engineer only £120-250

Parts commonly replaced

  • Room temperature sensor
  • Connecting cable/wiring loom
  • Control unit interface

Related codes

Full explanation for F.575
Showing 151–160 of 185
F.576

Your boiler is struggling to accurately detect the temperature inside your home, so it has decided to ignore your wall thermostat and run based on its internal settings instead.

Low Engineer only £120-220

Parts commonly replaced

  • Room temperature sensor
  • Connecting cable/wiring harness

Related codes

Full explanation for F.576
F.577

Your boiler is working normally, but it is currently unable to read the temperature for your secondary heating zone, so that specific part of your home may not be heating as accurately as usual.

Low Engineer only £120-200

Parts commonly replaced

  • Room temperature sensor
  • Communication module

Related codes

Full explanation for F.577
F.578

Your boiler has lost the connection to the temperature sensor for your secondary heating zone, so it is currently ignoring room-specific thermostat data for that area.

Low Engineer only £120-220

Parts commonly replaced

  • Room temperature sensor
  • Connecting cable/wiring loom

Related codes

Full explanation for F.578
F.579

Your boiler's secondary heating zone is unable to accurately measure the temperature in that specific part of your home due to a loose or damaged connection to a sensor.

Low Engineer only £120-200

Parts commonly replaced

  • Room temperature sensor
  • Wiring loom

Related codes

Full explanation for F.579
F.580

Your boiler is working normally, but it cannot currently track the temperature in one specific zone of your home because an optional room sensor is missing or disconnected.

Low Engineer only £120-200

Parts commonly replaced

  • Room temperature sensor
  • Communication module

Related codes

Full explanation for F.580
F.581

Your boiler has lost the signal from a temperature sensor used to regulate a specific heating zone, meaning it is currently heating your home based on pre-set timing rather than room temperature.

Low Engineer only £120-200

Parts commonly replaced

  • Room temperature sensor
  • Wiring harness

Related codes

Full explanation for F.581
F.582

Your boiler is struggling to accurately detect the temperature in a specific part of your home due to a wiring or sensor fault, but it will continue to heat your home using its internal settings.

Low Engineer only £120-220

Parts commonly replaced

  • Room temperature sensor
  • Connecting cable/wiring harness

Related codes

Full explanation for F.582
F.583

Your boiler is working normally, but it is unable to detect the temperature of a specific room, so it is currently heating your home without using that room's thermostat data.

Low Engineer only £120-200

Parts commonly replaced

  • Room temperature sensor
  • Communication module

Related codes

Full explanation for F.583
F.584

Your boiler is struggling to accurately read the temperature in one of your rooms due to a wiring or sensor issue, so it is running based on general settings instead.

Low Engineer only £120-220

Parts commonly replaced

  • Room temperature sensor
  • Connecting cable

Related codes

Full explanation for F.584
F.585

Your boiler has identified a minor fault with an external room temperature sensor for one of your heating zones, so it is simply ignoring that sensor and running based on its own internal temperature settings instead.

Low Engineer only £120-200

Parts commonly replaced

  • Room temperature sensor
  • Wiring loom

Related codes

Full explanation for F.585
Showing 161–170 of 185
F.666

Your boiler is struggling to communicate with a specific temperature sensor related to your solar hot water heating system.

Low Engineer only £120-220

Parts commonly replaced

  • DHW sensor TS3
  • Wiring harness for solar module

Related codes

Full explanation for F.666
F.667

Your boiler has detected a faulty connection to the solar water preheating sensor, which may prevent your hot water from being pre-warmed by solar energy.

Low Engineer only £150-250

Parts commonly replaced

  • DHW solar sensor
  • Wiring harness

Related codes

Full explanation for F.667
F.668

Your boiler is struggling to coordinate its hot water system because it has lost the signal from a sensor that monitors the heat coming from your solar panels.

Medium Engineer only £150-250

Parts commonly replaced

  • DHW sensor TS4
  • Wiring harness for solar module

Related codes

Full explanation for F.668
F.669

Your boiler's hot water preheating feature has detected a faulty electrical connection and has automatically switched it off to prevent incorrect operation.

Low Engineer only £150-250

Parts commonly replaced

  • DHW preheating sensor (TS4)
  • Wiring harness

Related codes

Full explanation for F.669
F.670

Your boiler is struggling to communicate with the sensor that tracks heat from your solar panels, meaning it cannot use stored solar energy to help heat your home.

Low Engineer only £120-200

Parts commonly replaced

  • Temperature sensor
  • Wiring harness

Related codes

Full explanation for F.670
F.671

Your boiler is having trouble communicating with the solar energy system that helps heat your home, likely due to a faulty electrical connection or sensor.

Low Engineer only £150-250

Parts commonly replaced

  • Buffer temperature sensor (TS3)
  • Wiring harness

Related codes

Full explanation for F.671
F.672

Your boiler is having trouble communicating with the solar energy component, meaning it cannot detect the temperature from your solar thermal panels.

Low Engineer only £150-250

Parts commonly replaced

  • Solar temperature sensor
  • Wiring harness

Related codes

Full explanation for F.672
F.673

Your boiler is having trouble communicating with your solar hot water system because of a faulty connection or sensor in that part of the setup.

Low Engineer only £120-250

Parts commonly replaced

  • Solar temperature sensor TS3
  • Wiring harness

Related codes

Full explanation for F.673
F.682

Your boiler has stopped working because it cannot properly measure the amount of air required for safe combustion.

High Engineer only £250-450

Parts commonly replaced

  • Air mass flow sensor
  • Gas valve
  • PCB

Related codes

Full explanation for F.682
F.683

Your boiler has detected an issue with the sensor that measures the air flow required for safe burning and has shut down to protect your system.

High Engineer only £200-350

Parts commonly replaced

  • Air mass flow sensor
  • Gas-air composite control unit
  • Wiring harness

Related codes

Full explanation for F.683
Showing 171–180 of 185
F.684

Your boiler has detected an issue with the air flow or exhaust system, meaning it has safely shut down to prevent unsafe gases from building up inside your home.

Emergency Engineer only £150-350

Parts commonly replaced

  • Flue gas sensor
  • Back draught safety device
  • PCB

Related codes

Full explanation for F.684
F.688

Your boiler's internal computer is experiencing a communication breakdown, causing it to run in a limited, backup mode that may result in loss of heating or hot water.

High Engineer only £250-500

Parts commonly replaced

  • MZIO Electronics Module
  • Communication Ribbon Cable

Related codes

Full explanation for F.688
F.693

Your boiler has stopped working because it has lost its connection to a safety sensor that monitors the temperature of the exhaust fumes.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

Full explanation for F.693
F.694

Your boiler has detected a safety concern with its exhaust system and has shut itself down to prevent any risk of overheating or unsafe operation.

Emergency Engineer only £180-350

Parts commonly replaced

  • Flue gas temperature sensor
  • Heat exchanger
  • Control unit

Related codes

Full explanation for F.694
F.696

Your boiler has stopped working because it cannot correctly read the temperature of the exhaust gases due to a faulty sensor or electrical connection.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

Full explanation for F.696
F.762

Your boiler has stopped working because the water pressure inside your heating system has dropped too low to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, which is a silver braided hose connecting two pipes near the boiler.
  2. Slowly open the valve(s) on the loop to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valve(s) tightly and check the display to see if the error has cleared.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

Full explanation for F.762
F.763

Your boiler has detected that the incoming gas supply pressure is higher than it is designed to handle, forcing it to shut down for safety.

Emergency Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Gas pressure regulator
  • Gas pressure switch

Related codes

Full explanation for F.763
F.764

Your boiler is connected to another unit that is reporting a problem, which is preventing your system from working correctly.

High Engineer only £150-350

Parts commonly replaced

  • Communication module
  • Cascading control board
  • Bus connection cable

Related codes

Full explanation for F.764
F.765

Your boiler is struggling to communicate with a secondary heating unit or an additional linked appliance, causing the system to stop working as a safety precaution.

High Engineer only £150-350

Parts commonly replaced

  • Communication cable
  • Bus communication module
  • Control PCB

Related codes

Full explanation for F.765
F.797

Your boiler has detected that the water pump responsible for circulating heat around your home and to your taps has stopped working correctly.

High Engineer only £250-450

Parts commonly replaced

  • Circulation pump
  • Pump wiring harness

Related codes

Full explanation for F.797
Showing 181–185 of 185
F.799

Your boiler has stopped working because the internal pump that circulates hot water is experiencing an electrical failure.

High Engineer only £250-450

Parts commonly replaced

  • Central heating circulation pump
  • Pump wiring harness
  • Boiler control board

Related codes

Full explanation for F.799
F.980

Your boiler has detected that the water pressure in your system is too low to safely heat your hot water, so it has stopped the hot water function to protect itself.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop connected to your boiler pipework.
  2. Open the filling valve slowly to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valve tightly to prevent over-pressurisation.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F.980
F.981

Your boiler has stopped producing hot water because the internal water pressure in your heating system has dropped too low to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, usually two silver valves connected by a flexible metal hose under the boiler.
  2. Open the valves slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both valves tightly and restart the boiler to clear the fault.

Parts commonly replaced

  • Pressure sensor
  • Filling loop assembly

Related codes

Full explanation for F.981
F.982

Your boiler has detected that the water pump responsible for circulating heat is not submerged in enough water, preventing it from heating your home or your taps.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F.982
P.4

Your boiler has detected that the water pressure is too low for it to operate safely and needs to be refilled.

High DIY-safe £0-120

What to check first

  1. Locate the external filling loop, which is usually a braided silver hose with two small valves.
  2. Slowly open both valves to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both valves tightly and the boiler should automatically reset and resume operation.

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for P.4
Status & diagnostic codes

17 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

I.56 Status Your boiler is currently receiving a signal from an external controller, such as a smart thermostat or a building management system, asking it to provide heating or hot water. I.57 Status Your boiler has been temporarily switched off by an external device, such as a smart home controller, an underfloor heating safety switch, or a frost protection unit. I.59 Status Your boiler has recently had its internal settings reset or restored to their factory defaults, which is usually a temporary status message rather than a breakdown. I.93 Status Your boiler has detected an internal communication issue between its electronic parts, which prevents it from operating correctly. P.1 Diagnostic Your boiler is simply reminding you that its scheduled annual service is now due to ensure it continues running safely and efficiently. P.8 Diagnostic Your boiler is simply reminding you that it has reached its scheduled running time and is now due for its routine annual service. S.9 Status Your boiler is currently performing a standard safety check before igniting, and this message indicates that the system is preparing to heat your home. S.29 Status Your boiler is operating normally and performing its standard heating function without any active issues. S.36 Status Your boiler is currently operating normally by pre-warming its internal water store to ensure you have hot water available as soon as you turn on the tap. S.59 Status Your boiler is currently performing a routine self-check on its exhaust temperature sensor and is temporarily pausing its normal operation to complete this test. S.60 Status Your boiler has automatically turned off the heating because the outside temperature is warm enough that it thinks your home doesn't need it. S.74 Status Your boiler is temporarily pausing the central heating because it is prioritising heating up your hot water tank. S.75 Status Your boiler is simply performing a routine process to keep hot water moving through your pipes and is not experiencing a fault. S.94 Status Your boiler is working fine but is currently waiting for a Signal from your secondary heating zone controls before it starts warming those specific radiators. S.95 Status Your boiler is working fine, but it is currently waiting for a signal from the third heating zone's thermostat before it starts heating that area. S.96 Status Your boiler is currently idle because it is waiting for a signal from an external device or a specific room control that is not currently requesting heat. S.154 Status Your boiler is temporarily pausing because it has detected that the heat it is producing isn't moving into your radiators or water tank efficiently enough.
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