Vaillant ecoTEC plus Fault codes & diagnostics

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

CombiSystemRegular Natural GasLPG 12-38 kW 2005-present
GC Numbers 47-044-3247-044-3347-044-3441-044-4841-044-4941-044-5041-044-5141-044-5247-044-5347-044-5447-044-5541-044-5841-044-5941-044-6041-044-6141-044-6247-044-8247-044-8347-044-8441-044-8541-044-8641-044-8741-044-8841-044-8947-044-9347-044-9447-044-9547-044-9641-044-7641-044-7741-044-7841-044-7941-044-80

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Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 53 High 6 Medium 63 Low

All 124 documented codes

Tap any card for details

con

Your boiler's control panel and its internal computer are not talking to each other, meaning the unit cannot receive instructions to provide heat or hot water.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Display Interface Module
  • Wiring harness

Related codes

d.00

Your boiler is simply displaying a status message telling you it is automatically adjusting its power output to best heat your home, rather than indicating a fault.

Low Engineer only
d.02

Your boiler is currently taking a mandatory rest period to prevent it from switching on and off too frequently, which is a normal protective feature.

Low Engineer only
d.05

The d.05 code is not actually an error; it is a normal status message showing the temperature your boiler is currently aiming to reach for your radiators.

Low DIY-safe

What to check first

  1. No action required
  2. This is a status code confirming your boiler is operating normally
  3. Press the 'i' button on the front panel to return to the standard display
d.08

Your boiler is currently receiving a signal from your room thermostat telling it that no heating is required at this moment.

Low DIY-safe

What to check first

  1. Check your room thermostat to ensure the target temperature is set higher than the current room temperature
  2. Ensure your thermostat is not in sleep or frost protection mode
  3. Check the battery levels in your wireless thermostat if applicable

Related codes

d.09

This is not a fault; it is simply a status message showing the current target temperature your thermostat is requesting from your boiler.

Low Engineer only
Showing 11–20 of 124
d.10

Your boiler is simply reporting the current activity status of its internal water pump to let you know if it is turned on or off.

Low Engineer only
d.11

Your boiler is simply reporting that a secondary pump, responsible for circulating water through your heating system, is currently not running.

Low DIY-safe £150-300

What to check first

  1. Check if your thermostat or heating controls are calling for heat
  2. Monitor the boiler display to see if the status changes when heating is activated
  3. Ensure any external zone valves or pumps are receiving power

Parts commonly replaced

  • Shunt pump
  • Pump wiring harness
  • Main PCB

Related codes

d.13

Your boiler is simply reporting that the internal pump responsible for moving hot water is currently resting or has just switched on.

Low Engineer only
d.16

Your boiler is correctly receiving a signal from your thermostat that the heating is currently turned off.

Low DIY-safe

What to check first

  1. Check your wall-mounted thermostat or smart app settings to ensure they are set to 'on' or 'active'
  2. Increase the target temperature on your room thermostat to see if the boiler status changes to 'on'
  3. Check batteries in your wireless thermostat unit if applicable

Related codes

d.17

Your boiler is currently configured to monitor the temperature of water returning from your heating system rather than the water leaving it, which is a specific setting typically used for underfloor heating systems.

Low Engineer only
d.19

This code is simply an information status display showing how your boiler's internal water pump is currently being told to operate, rather than an error or a fault with your heating system.

Low Engineer only
d.20

This code is not actually an error; it is a status message showing the current setting for your maximum hot water temperature.

Low Engineer only
d.21

This is not a fault; it simply indicates whether the comfort setting that keeps your tap water ready to heat instantly is currently turned on or off.

Low DIY-safe

What to check first

  1. Press the 'i' button on the boiler display to view system status
  2. Navigate to the warm start settings menu
  3. Select 'on' if you want instant hot water, or 'off' if you prefer to save energy

Related codes

Showing 21–30 of 124
d.22

Your boiler is simply reporting that it is currently not being asked to produce any hot water.

Low DIY-safe

What to check first

  1. This is a status code, not a fault, so no repair is required.
  2. If you have no hot water, check that your hot water tap is fully open and the boiler's target temperature is set correctly.
  3. Check your external thermostat or programmer to ensure a hot water timer is currently active.

Related codes

d.23

Your boiler is simply reporting that it is currently set to standby mode and is not being asked to provide heating or hot water.

Low DIY-safe

What to check first

  1. Check your room thermostat or boiler control panel to ensure the heating is switched to 'On'
  2. Increase the target temperature on your room thermostat to be higher than the current room temperature
  3. Ensure the central heating timer or programmer is currently set within an 'On' period

Related codes

d.24

Your boiler's internal water pressure sensor is telling the system that the water flow has stopped or the sensor itself is not detecting any movement, which usually prevents the heating from turning on.

High Engineer only £150-£300

Parts commonly replaced

  • Pressure sensor
  • Flow switch
  • Pump

Related codes

d.25

Your boiler is simply indicating that the 'warm start' or cylinder heating feature requested by your thermostat is currently turned off.

Low DIY-safe

What to check first

  1. Check your thermostat or boiler display settings to see if the 'warm start' or 'hot water comfort' function is disabled
  2. Toggle the setting to 'on' if you prefer your hot water to be kept warm for faster delivery
  3. No action is required if you are happy with how your hot water is currently functioning

Related codes

d.31

This code is simply an information display showing whether your boiler is set to fill itself automatically, semi-automatically, or requires you to do it manually.

Low DIY-safe

What to check first

  1. Navigate to the boiler's settings menu
  2. Locate the d.31 diagnostic menu
  3. Adjust the value to match your specific installation requirements, typically 1 if you have a built-in filling loop

Related codes

d.33

Your boiler is displaying the current operating speed of the fan, which is a normal status message rather than a breakdown.

Low Engineer only
d.35

Your boiler is currently reporting the status of the valve that switches your water flow between heating your home and heating your hot water tap.

Low Engineer only £150-250

Parts commonly replaced

  • Diverter valve cartridge
  • Diverter valve motor

Related codes

Showing 31–40 of 124
d.41

Your boiler is simply displaying the current temperature reading of the water returning to it from your radiators; this is an information code rather than a fault.

Low Engineer only
d.45

Your boiler is displaying a status code rather than a fault, indicating the current internal setting for how hot it should make your radiators based on the outside temperature.

Low Engineer only
d.50

Your boiler is displaying a diagnostic setting for its internal air fan rather than a breakdown error, but it may indicate an issue with the fan's operation or the circuit board settings.

Medium Engineer only £150-350

Parts commonly replaced

  • Fan unit
  • PCB (Printed Circuit Board)

Related codes

d.51

Your boiler is currently recalibrating its internal fan settings and is not reporting a failure; it is performing a routine adjustment rather than displaying an active heating breakdown.

Low Engineer only
Showing 41–50 of 124
d.60

Your boiler has detected that it is getting too hot and has switched itself off multiple times to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Pump
  • Diverter valve
  • Heat exchanger
  • NTC thermistor

Related codes

d.61

Your boiler has failed to light several times and is currently recording these failed attempts rather than performing an action.

Medium Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

d.66

This code simply confirms whether your boiler is currently set to keep a small amount of water pre-heated for faster hot water taps, rather than indicating a fault.

Low DIY-safe

What to check first

  1. Locate the menu button on your boiler display
  2. Navigate to the 'Comfort' or 'Warmstart' setting
  3. Select 'on' if you want faster hot water, or 'off' to save on energy costs
d.67

Your boiler is currently in a mandatory waiting period, purposely resting to prevent it from cycling on and off too frequently.

Low Engineer only
d.68

Your boiler is struggling to light itself on the first try and is keeping a record of these failed attempts.

Medium Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead

Related codes

d.69

Your boiler has failed to light the flame after two attempts and is currently tracking how many times this has happened.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Burner seal

Related codes

d.70

Your boiler is currently monitoring or testing the internal valve that decides whether to send hot water to your radiators or your taps.

Low Engineer only

Parts commonly replaced

  • Diverter valve
  • Diverter valve motor

Related codes

Showing 51–60 of 124
F.00

Your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water leaving the unit.

High Engineer only £90-160

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Wiring harness
  • PCB

Related codes

F.0

Your boiler has stopped working because it cannot accurately measure the temperature of the water leaving the unit due to a sensor or wiring connection fault.

High Engineer only £100-£220

Parts commonly replaced

  • Flow NTC Thermistor
  • NTC Wiring Harness
  • Main PCB

Related codes

F.01

Your boiler has stopped working because it cannot accurately measure the temperature of the water returning to the unit.

High Engineer only £100-£180

Parts commonly replaced

  • NTC Return Temperature Sensor
  • Sensor Wiring Harness

Related codes

F.1

Your boiler has stopped working because it cannot accurately measure the temperature of the water returning to the unit due to a faulty sensor or wiring.

High Engineer only £100-£220

Parts commonly replaced

  • Return NTC thermistor
  • NTC wiring harness
  • Main PCB

Related codes

F.10

Your boiler has detected an electrical fault with the internal sensor that monitors the water temperature leaving the unit, causing it to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Wiring harness/connector
  • PCB

Related codes

F.11

Your boiler has stopped working because it thinks the water returning to the unit is much hotter than it actually is, causing it to shut down for safety.

High Engineer only £100-£180

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Internal wiring loom
  • Main PCB

Related codes

F.12

Your boiler has lost the ability to measure the temperature of your hot water cylinder because of a faulty sensor or a wiring issue, meaning it cannot heat your water correctly.

High Engineer only £90-160

Parts commonly replaced

  • Hot water cylinder NTC sensor
  • Wiring harness

Related codes

F.13

Your boiler has detected an electrical fault with the sensor that monitors your hot water tank, meaning it cannot accurately tell if your water is hot enough.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water Cylinder NTC Sensor
  • Wiring Harness

Related codes

F.20

Your boiler has switched itself off because it has reached an unsafe temperature and needs to cool down.

High DIY-safe £100-280

What to check first

  1. Ensure all radiator valves are fully open to allow water to flow.
  2. Check the boiler pressure gauge and top up to 1.5 bar if it is too low.
  3. Press the 'Flame' or 'Reset' button and hold for one second to restart the system.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Main Heat Exchanger (Flushing)

Related codes

F.22

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two braided silver hoses or blue levers) underneath the boiler.
  2. Slowly open both valves until you hear water flowing and the pressure gauge reaches between 1.0 and 1.5 bar.
  3. Close both valves tightly and restart the boiler to clear the fault code.

Parts commonly replaced

  • Filling loop valves
  • Pressure sensor
  • Expansion vessel

Related codes

Showing 61–70 of 124
F.23

Your boiler has shut down because there is a significant difference between the water temperature leaving the boiler and the temperature returning to it, usually caused by a circulation problem.

High DIY-safe £100-£350

What to check first

  1. Ensure all radiator valves (TRVs) are fully open
  2. Check that the boiler pressure is between 1.0 and 1.5 bar
  3. Bleed your radiators to remove any trapped air

Parts commonly replaced

  • Circulation pump
  • NTC thermistor (temperature sensor)
  • Magnetic filter (cleaning)

Related codes

F.24

Your boiler has shut down because the internal water temperature is heating up much faster than it can be circulated away, usually meaning the water is stuck or the pump is struggling.

High DIY-safe £150-£350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the digital display.
  2. Ensure at least two or three radiator valves are turned fully open to allow water flow.
  3. Try resetting the boiler by pressing the flame symbol button to see if the fault clears.

Parts commonly replaced

  • Circulation pump
  • Flow and return thermistors
  • Main heat exchanger (flushing)

Related codes

F.25

Your boiler has shut itself down because the air being pushed out of the chimney pipe has become dangerously hot.

Emergency Engineer only £150-450

Parts commonly replaced

  • Heat exchanger
  • Flue gas NTC sensor
  • Primary heat exchanger cleaning kit
  • Burner seal

Related codes

F.27

Your boiler has sensed a flame when there shouldn't be one, so it has shut down as a safety precaution to prevent damage.

High Engineer only £150-350

Parts commonly replaced

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

Related codes

F.28

Your boiler is trying to light itself to provide heat, but it is failing to create a flame, likely because it is not getting enough gas or the spark isn't catching.

High DIY-safe £100-350

What to check first

  1. Check that your gas emergency control valve is open and any prepay meters have credit.
  2. Verify if other gas appliances in your home, like a hob, are working correctly.
  3. If it is freezing outside, check if your condensate pipe (the plastic pipe leading outside) is frozen and thaw it with warm water.
  4. Press the Reset button (the flame symbol with a cross) for one second.

Parts commonly replaced

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

Related codes

F.29

Your boiler was working but the flame went out and it cannot manage to light itself back up.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances (like a hob) are working to ensure gas is reaching the property
  2. Check if your gas meter has credit and the isolation valve is open
  3. Press the 'Reset' button (indicated by a flame with a line through it) for three seconds

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Lead

Related codes

F.32

Your boiler's fan is unable to spin at the correct speed, which prevents the boiler from safely clearing exhaust fumes and starting the ignition process.

High Engineer only £250-£450

Parts commonly replaced

  • Combustion Fan
  • PCB (Main Control Board)
  • Wiring harness

Related codes

F.33

Your boiler is struggling to breathe because it cannot properly detect the flow of air required for safe operation.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Venturi

Related codes

F.49

Your boiler has lost its ability to communicate with its external controls, such as your thermostat, due to an electrical glitch in the internal data wiring.

High Engineer only £100-250

Parts commonly replaced

  • eBUS cable
  • External controls receiver
  • PCB (Printed Circuit Board)

Related codes

F.61

Your boiler is unable to correctly control the flow of gas, causing it to shut down for safety purposes.

High Engineer only £250-£550

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Showing 71–80 of 124
F.62

Your boiler has detected that the gas valve is not closing as quickly as it should, preventing the unit from shutting down the burner safely.

Emergency Engineer only £250-£550

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

F.64

Your boiler has detected an internal communication error between its electrical sensors and the main control board, causing it to shut down for safety.

High Engineer only £180-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • NTC Temperature Sensors
  • Wiring Loom

Related codes

F.65

Your boiler's internal control board has become too hot and has shut down the system to prevent damage.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Display PCB

Related codes

F.67

Your boiler's electronic control board has detected a confusing signal from the flame sensor, causing the system to shut down for safety.

High Engineer only £280-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Electrode / Flame Sensor

Related codes

F.68

Your boiler is struggling to keep its flame burning steadily, causing it to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Burner
  • Ignition lead

Related codes

F.70

Your boiler’s control board has lost its identity settings, meaning the internal computer no longer knows which specific model it is supposed to be operating.

High Engineer only £100-£350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • User Interface Display Board

Related codes

F.71

Your boiler is struggling to accurately measure the water temperature leaving the unit, usually because a sensor has failed or become disconnected.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Return temperature sensor (NTC)
  • Wiring harness

Related codes

F.72

Your boiler has detected that the sensors measuring water temperature going in and out are giving conflicting readings, so it has shut down as a safety precaution.

High Engineer only £120-220

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Sensor wiring harness

Related codes

F.73

Your boiler is struggling to read how much water is in the system because of a sensor issue, which has caused it to stop working for your safety.

High Engineer only £130-220

Parts commonly replaced

  • Digital water pressure sensor
  • Sensor wiring harness

Related codes

Showing 81–90 of 124
F.74

Your boiler's internal sensor has detected that the water pressure is too high or the sensor itself is sending an incorrect reading.

High DIY-safe £120-200

What to check first

  1. Check the digital or manual pressure gauge; if it is above 2.5 bar, you need to reduce the pressure.
  2. Ensure both valves on the external filling loop are tightly closed to prevent more water entering.
  3. Bleed water from a radiator using a bleed key into a container until the pressure gauge returns to between 1.0 and 1.5 bar.

Parts commonly replaced

  • Water pressure sensor
  • Filling loop valve

Related codes

F.75

Your boiler is unable to sense water moving or pressure building when it tries to start up, which has caused it to shut down for safety.

High DIY-safe £180-350

What to check first

  1. Check the pressure gauge and ensure it is between 1.0 and 1.5 bar
  2. If pressure is too low, use the filling loop to top it up
  3. Reset the boiler to see if the fault clears

Parts commonly replaced

  • Water Pressure Sensor
  • Circulation Pump
  • Expansion Vessel

Related codes

F.76

Your boiler's safety sensor has detected that the main heating component is getting too hot, so the system has shut itself down to prevent damage.

High Engineer only £450-900

Parts commonly replaced

  • Thermal fuse
  • Heat exchanger
  • Wire harness

Related codes

F.77

Your boiler is struggling to push waste gases out through the flue or is unable to clear internal condensation water properly.

High Engineer only £120-350

Parts commonly replaced

  • Condensate pump
  • Flue gas non-return flap
  • Wiring harness

Related codes

F.78

Your boiler is having trouble communicating with an external hot water control component, meaning it doesn't know the temperature of the water heading to your taps.

High Engineer only £90-180

Parts commonly replaced

  • DHW NTC Sensor
  • External Link Box
  • Wiring harness

Related codes

F.83

Your boiler is firing up, but it doesn't detect the water getting hotter quickly enough, so it has shut down to prevent itself from overheating.

High DIY-safe £100-250

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the digital display
  2. Ensure all radiator valves (TRVs) are turned to the highest setting
  3. Top up the water pressure using the filling loop if it is too low

Parts commonly replaced

  • NTC Temperature Sensors
  • Heat Exchanger (Descaling)
  • Circulation Pump

Related codes

F.84

Your boiler is confused because its internal thermometers are giving conflicting readings and don't agree on how hot the water actually is.

High Engineer only £120-£250

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • NTC thermistor
  • Wiring harness

Related codes

F.85

Your boiler has stopped working because its internal thermometers are giving conflicting readings and believe they have been fitted to the wrong pipes.

High Engineer only £90-180

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • NTC cable harness

Related codes

F.86

Your boiler has stopped providing heat because a safety limit switch for your underfloor heating has been triggered or disconnected.

High Engineer only £90-180

Parts commonly replaced

  • Underfloor heating limit thermostat
  • Wiring harness
  • External pump

Related codes

F.87

Your boiler has detected a problem with the internal ignition components, meaning it cannot safely light the burner to provide heat or hot water.

High Engineer only £100-£250

Parts commonly replaced

  • Ignition electrodes
  • Wiring harness
  • Ionisation probe

Related codes

Showing 91–100 of 124
F.88

Your boiler has detected an electrical connection issue with the gas valve, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

F.89

Your boiler's main internal pump is not speaking correctly to the control board, preventing the system from circulating heat.

High Engineer only £180-450

Parts commonly replaced

  • Circulation pump
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

F.91

Your boiler has lost the ability to monitor the water temperature in your hot water cylinder due to an electrical connection fault.

High Engineer only £90-180

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor Wiring Harness

Related codes

F.92

Your boiler's internal computer is receiving the wrong information about its own identity, preventing it from running safely.

High Engineer only £100-£250

Parts commonly replaced

  • Coding Resistor
  • PCB (Printed Circuit Board)

Related codes

F.97

Your boiler's internal computer has failed a self-test and is no longer able to communicate with the rest of the system.

High Engineer only £300-£550

Parts commonly replaced

  • Main PCB (Printed Circuit Board)

Related codes

F.XX-F.XX

This code isn't an active fault but rather a menu view showing the history of past errors your boiler has experienced.

Low DIY-safe

What to check first

  1. Navigate through the menu using the plus and minus buttons to view the history
  2. Press the 'reset' button to clear active faults if the boiler is currently locked out
  3. No action is needed if the boiler is currently working correctly

Related codes

F22

Your boiler has stopped working because the water pressure is too low for it to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop handles (usually two blue or black taps) underneath the boiler.
  2. Slowly turn both handles 90 degrees to allow water into the system while watching the pressure gauge.
  3. Close both handles fully once the pressure reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor
F70

Your boiler's computer brains are not talking to each other correctly because a security code needs to be re-entered after a repair.

High Engineer only £80-120

Parts commonly replaced

  • Main PCB
  • User Interface display board
P.00

Your boiler is currently running an automatic program to remove trapped air from the system, which usually happens during startup or after maintenance.

Low DIY-safe

What to check first

  1. Wait approximately 6 to 7 minutes for the program to finish automatically
  2. Ensure your radiator valves are fully open to allow air to move
  3. Once the program ends, check if the water pressure is still within the green zone (1.0 to 1.5 bar)

Related codes

P.0

Your boiler is currently running a self-cleaning routine to remove trapped air bubbles from the system.

Low DIY-safe

What to check first

  1. Wait for the program to finish, which usually takes about 6.5 minutes.
  2. Ensure the small screw cap on the internal automatic air vent is slightly loosened.
  3. Check your boiler pressure gauge and top it up if it has dropped during the process.

Related codes

Showing 101–110 of 124
P.01

Your boiler has failed while running a specific test used for commissioning or high-power performance checks.

Medium DIY-safe £80-160

What to check first

  1. Turn the boiler power off at the wall or fused spur
  2. Wait 60 seconds
  3. Turn the power back on and press the 'Reset' button (indicated by a flame with a line through it)

Parts commonly replaced

  • None (usually a software/setting reset)
  • Printed Circuit Board (PCB)

Related codes

P.1

Your boiler is simply running a routine internal test to check it can operate at its maximum power level after starting up.

Low DIY-safe

What to check first

  1. Wait for the test to complete automatically
  2. Do not turn the boiler off while the code is displayed
  3. Monitor the display to ensure it returns to a normal temperature reading

Related codes

P.02

Your boiler is not in a fault state; it is simply running a pre-programmed test to check how it performs at its lowest power setting.

Low DIY-safe

What to check first

  1. Wait approximately 15 minutes for the program to finish automatically
  2. Press the 'Back' button (represented by a left-facing arrow) to manually exit the test
  3. Turn the boiler off and back on again if the screen remains stuck

Related codes

P.2

Your boiler is currently running a background self-test to check it can operate safely at its lowest power setting.

Low DIY-safe

What to check first

  1. Wait for the test to complete automatically (usually takes 15 minutes)
  2. Press the 'Back' or 'Reset' button if the boiler appears stuck after 20 minutes
  3. Turn the power off and back on at the fused spur switch to restart the system

Related codes

P.3

Your boiler is undergoing a temporary calibration process where it checks its heating settings; it is not a fault, but a normal status message.

Low DIY-safe

What to check first

  1. Wait approximately 15 minutes for the program to finish
  2. Ensure your radiator valves are open to allow heat flow during the test
  3. Monitor the display to see if it returns to a standard temperature reading

Related codes

P.4

Your boiler is currently running a safety program to remove trapped air from the internal pipes and heat exchanger.

Low DIY-safe

What to check first

  1. Wait for the program to finish, as it usually stops automatically after 5 to 10 minutes
  2. Ensure all radiator valves are fully open to help move air through the system
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped

Related codes

P.5

Your boiler is running a specialized internal test to ensure its safety sensor correctly shuts the system down if it gets too hot.

Low DIY-safe

What to check first

  1. Wait for the test to complete automatically
  2. Do not turn the boiler off during the process
  3. If the code persists, restart the boiler using the reset button

Related codes

P.06

Your boiler is currently running a self-check program to fill the heating system with water and is not experiencing a permanent fault.

Low DIY-safe

What to check first

  1. Wait approximately 15 minutes for the program to finish automatically
  2. Ensure your filling loop valves are closed once the pressure reaches 1.5 bar
  3. If the code persists, press and hold the 'Reset' button (flame icon) for 3 seconds

Related codes

P.6

Your boiler is currently running a self-diagnostic test to check the water pressure and fill level as it prepares to start up.

Low DIY-safe

What to check first

  1. Wait approximately 15 minutes for the program to finish
  2. Ensure your external or internal filling loop is closed
  3. Check that the pressure gauge is between 1.0 and 1.5 bar

Related codes

P.07

Your boiler is currently running a self-cleaning mode to remove trapped air bubbles from the pipes and pump.

Low DIY-safe

What to check first

  1. Wait approximately 5 to 10 minutes for the programme to finish automatically
  2. Ensure your radiator valves are fully open to help air move through the system
  3. Check the boiler pressure gauge and top up to 1.5 bar if it has dropped

Related codes

Showing 111–120 of 124
S.10

Your boiler is simply letting you know that it is currently busy heating up water for your taps or shower.

Low DIY-safe

What to check first

  1. No action required, this is a normal operating status and not a fault code.

Related codes

S.13

Your boiler is currently just starting the process to heat your water, so it is working normally and does not have a fault.

Low Engineer only
S.15

Your boiler is simply performing a routine cooling-down process after you last used hot water, and there is no fault with your system.

Low Engineer only
S.16

Your boiler is currently cooling down its internal components after you have finished using hot water, which is a normal part of its shutdown process.

Low Engineer only
S.33

Your boiler is currently performing a safety check on its internal airflow system and is waiting for a pressure sensor to confirm it is safe to ignite.

Medium Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Fan
  • Wiring harness

Related codes

S.97

Your boiler is currently performing an internal health check on its sensors and has temporarily paused heating and hot water to ensure everything is functioning safely.

Low DIY-safe

What to check first

  1. Wait up to 15 minutes for the automatic sensor test to finish
  2. Check the boiler's display for any further error codes once the test ends
  3. Monitor the boiler to ensure it returns to normal operation automatically

Parts commonly replaced

  • Water pressure sensor
  • Main PCB

Related codes

T.02

Your boiler is struggling to switch between providing hot water and heating your radiators because an internal valve is stuck or malfunctioning.

High Engineer only £180-£320

Parts commonly replaced

  • Three-way diverter valve
  • Diverter valve motor/actuator

Related codes

T.03

Your boiler's fan is struggling to start or run at the correct speed, which is preventing the boiler from firing up for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Extraction Fan
  • PCB (Printed Circuit Board)
  • Wiring Harness

Related codes

Showing 121–124 of 124
T.04

Your boiler is struggling to move heated water to your hot water cylinder, which means you may not have any hot water.

High Engineer only £180-£350

Parts commonly replaced

  • Cylinder charging pump
  • Pump cable/harness
  • PCB

Related codes

T.05

Your boiler's internal pump is having trouble moving water through the system, which is preventing it from providing heating or hot water.

High DIY-safe £220-450

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar on the digital display
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Bleed your radiators to remove any trapped air that might be blocking water flow

Parts commonly replaced

  • Circulation pump
  • Pump head
  • Automatic air vent

Related codes

T.06

Your boiler is struggling to push water around your radiators because an external pump is not working as expected.

High Engineer only £180-350

Parts commonly replaced

  • External central heating pump
  • Pump wiring harness
  • PCB (Printed Circuit Board)

Related codes

T.08

Your boiler is currently completing a routine check of its burner system while it is in the process of starting up.

Low DIY-safe

What to check first

  1. Wait for 2-5 minutes to see if the status code clears automatically
  2. Check that your gas supply is active at the meter
  3. Ensure your thermostat is calling for heat

Related codes

47 operating states & engineer diagnostics

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

D.000 Diagnostic Your boiler is currently set to run at a lower power level than its maximum capacity to save energy or match your home's heat demand. d.18 Diagnostic Your boiler is simply showing its current pump setting status rather than a fault; it indicates whether the pump is running constantly or only when needed. S.0 Status Your boiler is working perfectly fine and is simply in standby mode because your thermostat is not currently asking for the heating to be turned on. S.01 Status Your boiler is performing a normal startup procedure by clearing out the combustion chamber before it begins heating your home. S.1 Status Your boiler is preparing to ignite but is stuck at the stage where the internal fan is spinning up to clear the combustion chamber. S.02 Status Your boiler is simply preparing its internal pump before starting the heating process, which is a normal part of its operation. S.2 Status Your boiler is currently moving water through the system after a heating or hot water cycle to cool down the internal components safely. S.03 Status Your boiler is currently busy performing its normal start-up sequence to fire up the burner for heating. S.3 Status Your boiler is currently trying to light the flame to start provide heating or hot water, and this is a normal status message rather than a permanent error. S.04 Status Your boiler is currently working perfectly and is simply telling you that it is busy heating your radiators. S.4 Status Your boiler is operating normally and is currently in the process of starting up the burner to provide heat or hot water. S.05 Status Your boiler is briefly keeping the internal fan and pump running to safely cool down the heat exchanger after a heating cycle. S.5 Status Your boiler is pausing during its startup sequence while it waits for a signal that the fire has safely lit. S.06 Status Your boiler is temporarily running the internal fan to cool the system down after the heating has switched off. S.6 Status Your boiler's fan is continuing to run for longer than expected after the heating or hot water has finished. S.07 Status Your boiler is briefly running the pump after heating your radiators to safely move residual heat away from the unit. S.7 Status Your boiler is briefly keeping the internal pump running to safely circulate and dissipate leftover heat after you have finished using your heating or hot water. S.08 Status Your boiler is taking a short, normal break after finishing a heating cycle to prevent overheating and ensure everything cools down properly. S.8 Status Your boiler has reached the correct temperature and is taking a short, planned break to prevent it from switching on and off too frequently. S.14 Status Your boiler is working exactly as it should and is currently heating up the water for your taps. S.20 Status Your boiler is not broken; it is simply letting you know that it has received a request to provide hot water and is currently preparing to deliver it. S.21 Status Your boiler is briefly checking its fan and clearing the system before it starts heating your hot water. S.22 Status Your boiler is not broken; it is simply performing a routine preparation step to ensure everything is ready before it begins heating your water. S.23 Status Your boiler is currently preparing the burner to provide hot water, which is a normal part of its operation. S.24 Status Your boiler is working normally and is currently heating up your hot water. S.25 Status Your boiler is briefly cooling itself down after providing hot water and will resume normal operation in a few moments. S.26 Status Your boiler is simply running its internal fan for a short period to cool down after you have finished using hot water. S.27 Status Your boiler is briefly running the internal pump after providing hot water to help cool down the internal components. S.28 Status Your boiler has temporarily stopped the burner because it has reached the required temperature for hot water and is taking a short break to prevent overheating. S.30 Status Your boiler is working fine, but your external room thermostat or timer is telling it not to turn the heating on right now. S.31 Status Your boiler is working correctly but is currently ignoring heating requests because it is either set to summer mode or is waiting for a command from your external thermostat. S.32 Status Your boiler is struggling to start because the internal fan is not spinning at the correct speed required for a safe ignition. S.34 Status Your boiler has sensed the temperature is very cold and is automatically running to prevent the internal pipes from freezing. S.36 Status Your boiler is working fine, but your external thermostat or heating controls aren't telling it to turn on. S.39 Status Your boiler has received a signal from your underfloor heating system to stop running, likely because a safety thermostat has triggered to prevent the floor from getting too hot. S.41 Status Your boiler has detected that there is too much water in the system, which puts extra stress on the pipes and components. S.42 Status Your boiler has detected that a safety flap in the flue pipe is stuck closed, preventing exhaust gases from escaping. S.46 Status Your boiler has detected very cold temperatures and has automatically turned itself on at a low setting to prevent the internal pipes from freezing. S.53 Status Your boiler has temporarily stopped working because it has detected that water is the not moving through the system quickly enough to safely carry heat away. S.54 Status Your boiler has paused because it detects that water is not circulating quickly enough, often due to low pressure or an air pocket. S.88 Status Your boiler is currently running an automatic program to clear air bubbles out of the internal pipework and does not require a repair. S.91 Status Your boiler is currently set to a 'showroom' mode which allows the display to work for demonstration purposes but prevents the burner from actually firing to provide heating or hot water. S.96 Status Your boiler is temporarily paused because it is running a self-diagnostic check on its internal temperature sensors to ensure they are working correctly. S.98 Status Your boiler is temporarily paused because it has detected a potential issue with its internal sensors while performing a self-test. S.99 Status Your boiler is temporarily running a self-diagnostic check to ensure everything is working correctly and will resume normal operation shortly. S.108 Status Your boiler is currently performing a routine self-cleaning cycle to clear any fumes from the system before it attempts to ignite. S.109 Status Your boiler has temporarily stopped working because it has entered a standby mode, usually while it waits for a signal from your thermostat or because it needs to take a short break before restarting.