Vokera Syntesi 25 Fault codes & diagnostics

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

Combi Natural Gas 25 kW 2003-2010 Discontinued
GC Numbers 47-094-4647-094-6647-094-47

Replaced by: Vokera Vision

Download the Vokera Syntesi 25 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 73 High 8 Medium 5 Low
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-094-46 Syntesi 25 2003–2010
47-094-47 Syntesi 25 LPG 2003–2010
Just want the most common Vokera Syntesi 25 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 87 documented codes

Tap any card for details

01

Your boiler is unable to light the flame needed to heat your water and radiators, often due to a temporary interruption in the gas supply.

High DIY-safe £100-350

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm gas is reaching the property.
  2. Ensure your gas meter has credit if you use a pre-payment meter.
  3. Press the reset button on the boiler control panel and hold for a few seconds to try and restart the ignition sequence.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 01
1x

Your boiler is unable to light the gas or cannot tell that the flame is lit, so it has shut down for safety.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching the property
  2. Check your gas meter credit or ensuring the external gas valve is open
  3. Press the 'Reset' button on the control panel once to see if the boiler restarts

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve
  • PCB

Related codes

Full explanation for 1x
02

Your boiler has reached an unsafe temperature because the water is not circulating correctly through the system.

High DIY-safe £150-£350

What to check first

  1. Check that the isolation valves under the boiler are in the open position
  2. Ensure all radiator valves (TRVs) are turned up to full
  3. Try resetting the boiler using the control knob to see if the pump clears the blockage

Parts commonly replaced

  • Circulation Pump
  • Limit Thermostat
  • Main Heat Exchanger (if scaled)

Related codes

Full explanation for 02
2x

Your boiler has detected an internal electrical connection issue that is preventing it from running safely.

High Engineer only £90-250

Parts commonly replaced

  • Wiring harness
  • Printed Circuit Board (PCB)
  • Ignition electrode

Related codes

Full explanation for 2x
03

Your boiler has stopped working because the pipe that lets exhaust gases out is blocked or the internal sensor that checks for airflow is clogged with dirt.

High Engineer only £90-180

Parts commonly replaced

  • Fan
  • Air Pressure Switch
  • Venturi Tube
  • Flue Seals

Related codes

Full explanation for 03
3x

Your boiler has detected a problem with how it vents exhaust gases or manages air flow, causing it to shut down for safety.

High Engineer only £100-280

Parts commonly replaced

  • Fan
  • Air Pressure Switch
  • Venturi Tube
  • Flue Seals

Related codes

Full explanation for 3x
04

Your boiler has detected that the water pressure is too low to operate safely, which is usually caused by a leak or air trapped in the system.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (a flexible silver hose) underneath the boiler.
  2. Slowly open the one or two taps on the hose until you hear water flowing.
  3. Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Automatic air vent

Related codes

Full explanation for 04
4x

Your boiler has detected that the water pressure is too low for it to operate safely and has shut down to protect the system.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver braided hose under the boiler).
  2. Slowly open the valve or valves until you hear water entering the system.
  3. Watch the pressure gauge and close the valves once it reaches between 1.0 and 1.5 bar.
  4. Press the 'Reset' button on the control panel to restart the boiler.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for 4x
05

Your boiler is having trouble 'talking' to your wall-mounted thermostat or remote control unit.

High Engineer only £90-180

Parts commonly replaced

  • Remote control unit (RC05)
  • Connecting wiring
  • Main PCB

Related codes

Full explanation for 05
5x

Your boiler's central computer has encountered an internal error and can no longer control the heating or hot water safely.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 5x
Showing 11–20 of 87
06

Your boiler is having trouble measuring the temperature of your hot water, which is likely causing your taps and showers to stay cold.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Thermistor (NTC Sensor)
  • Wiring harness connecting to the sensor

Related codes

Full explanation for 06
6x

Your boiler has detected a fault with the temperature sensor that controls your hot water, meaning your water may not reach the correct temperature or might not heat up at all.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Thermistor
  • Wiring harness

Related codes

Full explanation for 6x
07

Your boiler's internal temperature sensor is failing to provide a reading, which means the system has shut down to prevent overheating.

High Engineer only £90-160

Parts commonly replaced

  • Primary NTC thermistor
  • Wiring harness

Related codes

Full explanation for 07
7x

Your boiler has detected that the water temperature in your central heating pipes is getting too hot or is not flowing correctly.

High Engineer only £90-180

Parts commonly replaced

  • Central Heating NTC Sensor
  • Circulation Pump
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 7x
8x

Your boiler's main internal computer has developed a malfunction and can no longer control the heating system safely.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 8x
09

Your boiler's electronic control board has developed a fault, meaning the internal computer can no longer communicate with the rest of the system.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 09
9x

Your boiler has stopped working because the waste water pipe is backed up or blocked, often due to freezing weather or a buildup of debris.

High DIY-safe £80-140

What to check first

  1. Locate the plastic condensate discharge pipe leading outside your property.
  2. Check if the pipe is frozen and gently pour warm (not boiling) water over it to melt the ice.
  3. Verify if the external end of the pipe is blocked by debris or submerged in water and clear it.
  4. Restart the boiler by turning the mode selector switch to the 'reset' position.

Parts commonly replaced

  • Condensate trap
  • Condensate discharge pipework
  • Float switch

Related codes

Full explanation for 9x
10

Your boiler is attempting to start but is unable to light the burner, meaning it cannot provide you with heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 10
11

Your boiler has detected a flame inside when it should be turned off, which prevents it from operating safely.

Emergency Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Ignition board
  • Flame sensor

Related codes

Full explanation for 11
12

Your boiler is attempting to restart its ignition process because it failed to light or maintain a flame.

High DIY-safe £100-350

What to check first

  1. Check if your gas supply is turned on and other gas appliances are working
  2. Press the reset button or turn the selector switch to 'OFF/RESET' for several seconds
  3. Ensure the condensate pipe (the white plastic pipe outside) isn't frozen if it is winter

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 12
Showing 21–30 of 87
13

Your boiler has detected an electrical communication problem within its internal wiring which is preventing it from running safely.

High Engineer only £120-280

Parts commonly replaced

  • Wiring harness
  • Main PCB
  • Control board connectors

Related codes

Full explanation for 13
13/14

Your boiler has detected an issue with the internal electrical connections that prevents it from operating safely.

High Engineer only £120-250

Parts commonly replaced

  • Wiring harness
  • PCB (Printed Circuit Board)
  • Sensor connections

Related codes

Full explanation for 13/14
14

Your boiler has detected an internal communication problem between its electronic components and is unable to fire up.

High Engineer only £100-280

Parts commonly replaced

  • Wiring Harness
  • Main Control Board (PCB)

Related codes

Full explanation for 14
15

Your boiler thinks it sees a flame even though it hasn't started the ignition process yet, which is causing it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation Probe
  • Printed Circuit Board (PCB)
  • Gas Valve

Related codes

Full explanation for 15
20

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • High limit thermostat
  • Pump
  • PCB

Related codes

Full explanation for 20
20/21/22

Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent overheating.

High Engineer only £180-350

Parts commonly replaced

  • NTC Temperature Sensor
  • Circulation Pump
  • Primary Heat Exchanger

Related codes

Full explanation for 20/21/22
21

Your boiler has detected a loose or faulty electrical connection inside its control system, which is preventing it from communicating with its internal components correctly.

High Engineer only £120-250

Parts commonly replaced

  • Wiring harness
  • PCB (Printed Circuit Board)
  • Connector block

Related codes

Full explanation for 21
22

Your boiler has detected a loose or faulty electrical connection inside its casing, meaning it has safely shut down to prevent potential damage.

High Engineer only £120-220

Parts commonly replaced

  • Wiring harness
  • Main printed circuit board

Related codes

Full explanation for 22
23

Your boiler has detected an internal communication problem between its electronic components or a possible electrical connection fault.

High Engineer only £120-350

Parts commonly replaced

  • Wiring harness
  • Printed Circuit Board (PCB)
  • Internal sensors

Related codes

Full explanation for 23
23/31

Your boiler has detected that some of its internal electrical connections or sensors are not communicating correctly, causing the system to stop working to avoid potential damage.

High Engineer only £120-250

Parts commonly replaced

  • Wiring harness
  • PCB (Printed Circuit Board)
  • Air pressure switch sensor

Related codes

Full explanation for 23/31
Showing 31–40 of 87
24

Your boiler has detected that the water inside the unit has become dangerously hot and has shut itself down to prevent damage.

High Engineer only £120-200

Parts commonly replaced

  • NTC temperature sensor
  • Central heating pump
  • Plate heat exchanger

Related codes

Full explanation for 24
25

Your boiler has detected a temporary internal communication error or a logic conflict and is likely attempting a self-correction or restart.

Low DIY-safe £0-120

What to check first

  1. Turn the boiler mode selector switch to the 'OFF/RESET' position.
  2. Wait for approximately 10 seconds.
  3. Turn the switch back to either the 'Heating & Hot Water' or 'Hot Water Only' position.

Parts commonly replaced

  • None (usually software reset)
  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 25
26

Your boiler has detected that the water returning to it is too hot, so it has safely shut itself down to prevent internal damage.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC sensor
  • Primary heat exchanger
  • Pump

Related codes

Full explanation for 26
27

Your boiler has detected an internal electronic communication error or a temporary sensor discrepancy and has paused operation for safety.

Medium DIY-safe £120-280

What to check first

  1. Turn the mode selector knob to the 'OFF/RESET' position.
  2. Wait for 30 seconds.
  3. Turn the knob back to the 'ON' or 'Winter' position to see if the error clears.

Parts commonly replaced

  • Main PCB (Control Board)
  • Thermistor (NTC Sensor)

Related codes

Full explanation for 27
28

Your boiler has detected that the water is not circulating correctly between the heating system and the boiler, which has caused it to shut down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Central heating pump
  • Flow/Return sensors
  • Primary heat exchanger

Related codes

Full explanation for 28
29

Your boiler's internal computer has lost its connection to one of the main components, likely due to a loose or damaged electrical cable.

High Engineer only £120-220

Parts commonly replaced

  • Wiring harness
  • PCB

Related codes

Full explanation for 29
30

Your boiler's computer has lost its internal configuration settings, meaning it has forgotten how to operate correctly.

High Engineer only £120-250

Parts commonly replaced

  • PCB (Main Control Board)

Related codes

Full explanation for 30
31

Your boiler is experiencing a communication or configuration error between internal electronic boards that prevents it from starting correctly.

High Engineer only £140-£350

Parts commonly replaced

  • Main PCB
  • Display Interface Board
  • Wiring Harness

Related codes

Full explanation for 31
32

Your boiler has stopped working because the internal fan, which safely exhausts gases out of the flue, is not spinning at the correct speed or has failed completely.

High Engineer only £200-£450

Parts commonly replaced

  • Fan assembly
  • Main circuit board (PCB)
  • Fan wiring harness

Related codes

Full explanation for 32
32/34

Your boiler has stopped working because it cannot properly clear exhaust gases, meaning it is currently unable to safely provide heating or hot water.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 32/34
Showing 41–50 of 87
33

Your boiler is struggling to clear exhaust gases safely, so it has stopped working to prevent any risk of fumes entering your home.

High Engineer only £150-300

Parts commonly replaced

  • Fan unit
  • Venturi
  • PCB

Related codes

Full explanation for 33
33/35

Your boiler's air circulation fan has failed, which means the machine has safely shut down because it cannot vent gasses properly.

High Engineer only £180-350

Parts commonly replaced

  • Fan unit
  • PCB
  • Wiring harness

Related codes

Full explanation for 33/35
34

Your boiler is failing to start because it cannot sense that the internal air circulation system is running correctly.

High Engineer only £150-250

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Wiring harness

Related codes

Full explanation for 34
35

Your boiler has stopped working because the internal fan, which safely clears exhaust gases, isn't spinning or communicating correctly with the system.

High Engineer only £180-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air pressure switch

Related codes

Full explanation for 35
36

Your boiler's main internal computer has detected a technical error and has stopped working to protect the system.

High Engineer only £250-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Control Board

Related codes

Full explanation for 36
37

Your boiler has detected that the internal fan is spinning too fast, which is preventing the system from starting safely.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 37
38

Your boiler’s internal computer has lost its programmed settings and no longer knows how to operate correctly.

High Engineer only £100-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Control Knob set

Related codes

Full explanation for 38
40

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

High DIY-safe £80-120

What to check first

  1. Locate the filling loop, which is a silver braided hose with one or two small valves under the boiler.
  2. Open the valves slowly to allow water into the system until the pressure gauge on the front of the boiler reaches 1.5 bar.
  3. Close the valves firmly and check the gauge to ensure it stays stable.

Parts commonly replaced

  • Pressure relief valve
  • Pressure gauge
  • Expansion vessel

Related codes

Full explanation for 40
41

Your boiler has detected a temporary internal communication issue or a potential sensor error and is trying to reset itself.

Low DIY-safe £0-120

What to check first

  1. Turn the control knob to the 'OFF/RESET' position.
  2. Wait for approximately 30 seconds.
  3. Turn the knob back to your desired 'Heating' or 'Hot Water' setting.

Parts commonly replaced

  • Temperature sensor (NTC thermistor)
  • Wiring harness

Related codes

Full explanation for 41
42

Your boiler's internal sensor that detects water pressure is not sending a signal, which prevents the boiler from starting safely.

High Engineer only £150-250

Parts commonly replaced

  • Pressure transducer
  • Wiring harness

Related codes

Full explanation for 42
Showing 51–60 of 87
50

Your boiler's internal computer has encountered a memory or software error that prevents it from running safely.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Control Knob Potentiometers

Related codes

Full explanation for 50
50-59

Your boiler's main control computer is experiencing a critical internal fault, which is preventing it from operating safely.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Interface board

Related codes

Full explanation for 50-59
50/51/52

Your boiler has detected an internal computer error that is causing it to shut down for safety reasons.

High Engineer only £150-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 50/51/52
51

Your boiler's internal computer has encountered a memory or software error that prevents it from running safely.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Control Knob Potentiometers

Related codes

Full explanation for 51
52

Your boiler's internal computer has encountered a memory or software error that prevents it from running safely.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Control Knob Potentiometers

Related codes

Full explanation for 52
53

Your boiler's electronic control board has detected an internal computer error and has shut down as a safety precaution.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 53
53/54/55/56

Your boiler has detected an internal computer error that is preventing it from operating safely.

High Engineer only £150-350

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness

Related codes

Full explanation for 53/54/55/56
54

Your boiler's electronic control board has detected an internal computer error and has shut down as a safety precaution.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 54
56

Your boiler's electronic control board has detected an internal computer error and has shut down as a safety precaution.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 56
60

Your boiler is experiencing a temporary communication error or a sensor timing issue that is causing it to pause current operations.

Medium DIY-safe £100-250

What to check first

  1. Press the reset button on the front control panel
  2. Turn the selector switch to the 'OFF/RESET' position and then back to 'ON'
  3. Monitor the boiler to see if the error code clears and operation resumes

Parts commonly replaced

  • Thermistor (NTC Sensor)
  • Main Control Board

Related codes

Full explanation for 60
Showing 61–70 of 87
60/61

Your boiler has stopped working because it is unable to accurately read the temperature of the water inside the system.

High Engineer only £120-200

Parts commonly replaced

  • NTC Thermistor
  • Wiring harness

Related codes

Full explanation for 60/61
61

Your boiler's internal temperature sensors are struggling to read the water temperature correctly, preventing the system from heating up properly.

High Engineer only £90-160

Parts commonly replaced

  • NTC Thermistor
  • Flow Sensor
  • Return Sensor

Related codes

Full explanation for 61
62

Your boiler has detected an internal electrical communication error or a wiring issue, which is preventing it from running safely.

High Engineer only £120-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Wiring Harness

Related codes

Full explanation for 62
70

Your boiler is having trouble reading the temperature of the water being sent to your radiators, which has caused it to stop heating your home to stay safe.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness

Related codes

Full explanation for 70
70/72/74

Your boiler is struggling to circulate water, likely because the internal valves are shut or the internal pump has seized up.

High Engineer only £120-250

Parts commonly replaced

  • Circulation pump
  • Flow sensor
  • Diverter valve

Related codes

Full explanation for 70/72/74
71

Your boiler has detected an internal communication or temperature sensor error that is currently preventing it from running normally.

High DIY-safe £120-280

What to check first

  1. Turn the mode selector switch to the 'OFF/RESET' position.
  2. Wait for approximately 30 seconds.
  3. Turn the switch back to the 'ON' or heating/hot water position.

Parts commonly replaced

  • NTC Temperature Sensor
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 71
71/73

Your boiler is struggling to accurately detect or manage the temperature of the water flowing through the system.

High Engineer only £150-250

Parts commonly replaced

  • NTC temperature sensor
  • PCB control board

Related codes

Full explanation for 71/73
72

Your boiler is having trouble reading the temperature of the water returning to it, which prevents it from heating your home correctly.

Medium Engineer only £120-220

Parts commonly replaced

  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for 72
73

Your boiler has detected an unusual temperature reading or a possible blockage that is preventing water from circulating correctly.

High Engineer only £120-280

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Circulation pump

Related codes

Full explanation for 73
74

Your boiler is unable to move water around the system because either the main pump is stuck or the internal valves are blocked.

High Engineer only £180-350

Parts commonly replaced

  • Circulation pump
  • Diverter valve
  • Flow switch

Related codes

Full explanation for 74
Showing 71–80 of 87
75

Your boiler has detected an internal electrical communication error or a wiring issue that is preventing it from working safely.

High Engineer only £100-£350

Parts commonly replaced

  • Wiring harness
  • Main PCB
  • Ignition transformer

Related codes

Full explanation for 75
75/76

Your boiler is having difficulty communicating with its internal controls due to a connection issue within its wiring, which means it has safely shut down to prevent incorrect operation.

High Engineer only £120-220

Parts commonly replaced

  • Wiring harness
  • PCB (Printed Circuit Board)
  • Sensor wiring loom
Full explanation for 75/76
76

Your boiler has detected an internal electrical communication error or a wiring issue that is preventing it from working safely.

High Engineer only £100-£350

Parts commonly replaced

  • Wiring harness
  • Main PCB
  • Ignition transformer

Related codes

Full explanation for 76
77

Your boiler has detected that the water temperature in your underfloor heating circuit has become too hot and has shut down as a safety precaution.

High Engineer only £120-250

Parts commonly replaced

  • Underfloor heating limit thermostat
  • Pump for underfloor circuit
  • PCB

Related codes

Full explanation for 77
78

Your boiler has detected a temporary internal communication error or a sensor synchronization issue that is preventing it from running properly.

High DIY-safe £100-280

What to check first

  1. Turn the selector switch to the 'OFF/RESET' position.
  2. Wait for approximately 30 seconds.
  3. Turn the selector switch back to the 'ON' position (Heating and Hot Water icon).

Parts commonly replaced

  • Domestic Hot Water (DHW) Thermistor
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 78
79

Your boiler has detected that the water is not circulating correctly between the heating pipes, preventing it from heating your home efficiently.

High Engineer only £150-300

Parts commonly replaced

  • Circulation pump
  • System filter
  • Diverter valve

Related codes

Full explanation for 79
80

Your boiler is experiencing a temporary communication error or initialization issue that may prevent it from starting correctly.

Medium DIY-safe £100-220

What to check first

  1. Locate the mode selector switch on the front of the boiler.
  2. Turn the switch to the 'OFF/RESET' position and wait for 5 seconds.
  3. Turn the switch back to either 'Hot Water Only' or 'Heating and Hot Water' to restart the system.

Parts commonly replaced

  • Main Control PCB
  • Wiring harness

Related codes

Full explanation for 80
80-83

Your boiler has detected a problem with its internal brain or main control panel, preventing it from functioning correctly.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Loom

Related codes

Full explanation for 80-83
80/90/91

Your boiler has detected an internal electronic error that is preventing it from operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for 80/90/91
83

Your boiler is experiencing a communication error between its internal parts, which it is currently trying to resolve automatically.

Low DIY-safe £100-£250

What to check first

  1. Wait up to 15 minutes for the boiler to self-correct
  2. Turn the selector switch to the 'Reset' position, wait for two seconds, and turn it back to the 'On' position
  3. Check if the boiler pressure is between 1 and 1.5 bar on the gauge

Parts commonly replaced

  • Main Control PCB
  • Wiring Loom

Related codes

Full explanation for 83
Showing 81–87 of 87
90

Your boiler has paused operation due to a temporary internal communication or sensor error that may clear itself or indicate a service is needed.

Low DIY-safe £0-120

What to check first

  1. Turn the selector switch to the 'OFF/RESET' position.
  2. Wait approximately 30 seconds.
  3. Turn the selector switch back to either the 'Heating' or 'Hot Water' position.

Parts commonly replaced

  • NTC Temperature Sensor
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 90
91

Your boiler has detected a temporary service issue that is preventing it from completing its ignition sequence, though it may resolve itself or require a simple reset.

Medium DIY-safe £80-160

What to check first

  1. Locate the mode selector switch on the front panel
  2. Turn the dial to the 'OFF/RESET' position and wait for 5 seconds
  3. Turn the dial back to the original winter or summer position to see if the error clears

Parts commonly replaced

  • Ignition module
  • Flame sensing electrode

Related codes

Full explanation for 91
92

Your boiler has detected that waste water produced during operation is not draining away properly, which is causing it to shut down to prevent damage.

High Engineer only £120-200

Parts commonly replaced

  • Condensate trap
  • Condensate pipework
  • Siphon

Related codes

Full explanation for 92
93

Your boiler is experiencing a temporary communication or sensor error that may resolve itself but often indicates a part is beginning to fail.

Medium DIY-safe £100-280

What to check first

  1. Press the reset button to clear the temporary error
  2. Monitor the boiler for recurring faults
  3. Ensure power supply to the boiler is stable
  4. Contact a Gas Safe engineer if the code persists

Parts commonly replaced

  • Main PCB
  • NTC Sensor
  • Wiring loom

Related codes

Full explanation for 93
93/95

Your boiler is unable to drain away water produced during normal operation because the waste pipe is obstructed, causing the system to stop working to prevent internal damage.

High DIY-safe £80-150

What to check first

  1. Locate the plastic pipe exiting the bottom of the boiler that leads to a drain or soakaway.
  2. Inspect the external end of the pipe for blockages, such as leaves, debris, or ice if it is winter.
  3. Ensure the pipe is not bent or kinked and flows freely into your household drainage system.

Parts commonly replaced

  • Condensate trap
  • Condensate pipework assembly
Full explanation for 93/95
94

Your boiler is having trouble communicating with a sensor that monitors its internal water drainage system, which is preventing it from running safely.

High Engineer only £120-220

Parts commonly replaced

  • Condensate sensor
  • Main control board

Related codes

Full explanation for 94
95

Your boiler has detected a temporary internal communication or processing error and is attempting to resolve itself.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to complete its current operation and reset the code automatically
  2. Turn the mode selector knob to the 'OFF/RESET' position and then back to 'ON'
  3. Ensure there is a constant power supply to the unit without frequent switching

Parts commonly replaced

  • None (Software reset)
  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 95
Status & diagnostic codes

1 operating states & engineer diagnostics

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

CO Diagnostic Your boiler is currently running in a special engineer-only testing mode for checking gas emissions and is not experiencing a mechanical fault.