Baxi Profile Fault codes & diagnostics

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

Regular Natural Gas 11-23 kW 1988-2003 Discontinued

Replaced by: Potterton Profile Prima

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
115 High 6 Medium 8 Low
Just want the most common Baxi Profile faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 129 documented codes

Tap any card for details

LED / flash-pattern codes
1 green flash

Your boiler has reached its set temperature and is temporarily resting because your home is already warm enough.

Low DIY-safe

What to check first

  1. Check your room thermostat is set to the desired temperature
  2. Wait for the temperature to drop naturally; the boiler will restart automatically when heat is needed
  3. No further action is required as this is normal operation
Full explanation for 1 green flash
1 red flash

Your boiler has likely overheated or a sensor has failed, causing the system to shut down for safety.

High DIY-safe £120-250

What to check first

  1. Check that all radiator valves are open to ensure water can flow.
  2. Allow the boiler to cool down for at least 20 minutes.
  3. Press the reset button or turn the mains power off and back on.

Parts commonly replaced

  • Overheat Thermostat
  • Temperature Sensor (Thermistor)
  • Circulation Pump

Related codes

Full explanation for 1 red flash
2 red flashes

Your boiler has become too hot and has automatically shut down to prevent damage or safety issues.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are open to allow water to circulate.
  2. Ensure your system pressure is at the correct level (usually 1 to 1.5 bar).
  3. Once the boiler has cooled down, press the reset button on the front or underside of the unit.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Thermistor

Related codes

Full explanation for 2 red flashes
3 green flashes

Your boiler has temporarily lost its flame and is currently trying to restart itself automatically.

Medium DIY-safe £90-250

What to check first

  1. Check that your external gas supply is turned on (e.g. at the meter)
  2. Wait for the boiler to attempt an automatic reset
  3. Monitor the display to see if the code clears or turns to a solid red fault

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for 3 green flashes
3 red flashes

Your boiler has tried to start up several times but cannot create a flame, meaning your heating and hot water will not work until it is reset or repaired.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to ensure gas is reaching the property
  2. Check if your gas meter has credit
  3. Turn the selector switch to the reset position for five seconds, then turn it back to the 'on' position

Parts commonly replaced

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

Related codes

Full explanation for 3 red flashes
4 green flashes

Your boiler is having a temporary moment of confusion between its internal brains, but it should fix itself automatically in a few minutes.

Low DIY-safe £0-120

What to check first

  1. Wait up to 10 minutes for the boiler to automatically reset the communication error
  2. Turn the power switch to the boiler off and back on again once
  3. Ensure there is no heavy electrical interference appearing near the boiler casing

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Interface

Related codes

Full explanation for 4 green flashes
5 green flashes

Your boiler's internal computer has had a temporary communication glitch and is attempting to restart itself.

Low DIY-safe £180-350

What to check first

  1. Wait up to 10 minutes for the boiler to automatically self-reset
  2. Switch the main electrical power to the boiler off and back on again
  3. Ensure your household electricity supply is stable and not fluctuating

Parts commonly replaced

  • Printed Circuit Board (PCB)
Full explanation for 5 green flashes
5 red flashes

Your boiler's computer memory has developed a internal communication error and can no longer read its own settings.

High Engineer only £180-350

Parts commonly replaced

  • Parameter Storage Unit (PSU)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 5 red flashes
6 green flashes

Your boiler has encountered a minor temporary glitch and is currently pausing before it attempts to restart itself automatically.

Low DIY-safe £60-120

What to check first

  1. Wait up to 15 minutes to see if the boiler resets itself automatically
  2. Ensure your decorative door or case is fully closed as some models have a safety cutout
  3. Check that your external heating controls or thermostat are calling for heat

Parts commonly replaced

  • External controls
  • Wiring connections

Related codes

Full explanation for 6 green flashes
Showing 11–20 of 129
6 red flashes

Your boiler has detected an internal communication or electrical problem that is preventing it from starting up safely.

High Engineer only £120-280

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness
  • Ignition Lead

Related codes

Full explanation for 6 red flashes
FLASH OFF FLASH

Your boiler has stopped working because the electrical power coming from your home supply is too low for it to run safely.

High Engineer only £100-280

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Power Supply Cable

Related codes

Full explanation for FLASH OFF FLASH
FLASH OFF ON

Your boiler has become too hot and has automatically shut down for safety purposes to prevent damage to the internal components.

High DIY-safe £120-350

What to check first

  1. Check all radiator valves are open and not turned off.
  2. Ensure there is enough water pressure in the system by checking the gauge if visible.
  3. Allow the boiler to cool down, then press the reset button or turn the mains power off and back on.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Temperature Sensors (NTC Thermistors)
Full explanation for FLASH OFF ON
FLASH ON FLASH

Your boiler's internal computer has encountered a fault and is unable to manage the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for FLASH ON FLASH
FLASH ON ON

Your boiler's internal computer has developed a fault and is no longer able to control the heating process safely.

High Engineer only £220-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Box

Related codes

Full explanation for FLASH ON ON
ON FLASH FLASH

Your boiler has detected that water isn't moving through the system properly or there isn't enough water inside, causing it to overheat and shut down for safety.

High DIY-safe £120-350

What to check first

  1. Check the pressure gauge and top up to 1.5 bar if it is low
  2. Ensure all radiator valves and isolation valves are fully open
  3. Bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Flow/Return Thermistors

Related codes

Full explanation for ON FLASH FLASH
ON FLASH ON

Your boiler has detected a problem with its temperature sensor, which means it cannot safely tell how hot the water is and has stopped working as a precaution.

High Engineer only £90-160

Parts commonly replaced

  • NTC Thermistor
  • Wiring harness

Related codes

Full explanation for ON FLASH ON
ON OFF FLASH

Your boiler has detected an electrical wiring issue where the power supply wires are connected the wrong way around, preventing it from starting safely.

High Engineer only £80-140

Parts commonly replaced

  • External wiring connection
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ON OFF FLASH
ON ON FLASH

Your boiler's internal computer has encountered a fault and is unable to control the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Box
Full explanation for ON ON FLASH
Digital codes
110

Your boiler has become too hot and has switched itself off as a safety precaution, often because air is trapped in the system preventing water from flowing properly.

High DIY-safe £80-160

What to check first

  1. Switch off the boiler and allow the system to cool down completely
  2. Use a radiator key to bleed any trapped air from all radiators, starting with the lowest floor
  3. Check your boiler pressure gauge and top it up to 1.5 bar if it has dropped
  4. Press the reset button on the front of the boiler

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Temperature Sensors (NTC Thermistors)

Related codes

Full explanation for 110
117

Your boiler has too much water in the system, which puts unnecessary stress on the internal components and pipes.

Medium DIY-safe £80-160

What to check first

  1. Check that the silver filling loop valves are tightly closed
  2. Bleed a radiator from a bottom-floor valve to release system pressure
  3. Monitor the pressure gauge until it returns to between 1.0 and 1.5 bar
  4. Restart the boiler once the pressure is stabilised

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for 117
118

Your boiler has stopped working because the water level inside the system is not high enough to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (a flexible silver hose) under the boiler.
  2. Slowly open the valve(s) until you hear water entering.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the valves tightly.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for 118
119

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver braided hose with two small taps) underneath or near the boiler.
  2. Slowly open both taps until you hear water entering the system.
  3. Watch the pressure gauge and close both taps tightly once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for 119
125

Your boiler has detected that water is not moving through the system correctly, which is causing it to overheat and shut down for safety.

High DIY-safe £180-450

What to check first

  1. Check if your radiator valves are open
  2. Ensure your system pressure is between 1 and 1.5 bar on the pressure gauge
  3. Gently bleed your radiators to remove trapped air

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor
  • External System Filter

Related codes

Full explanation for 125
127

Your boiler has failed to heat the water storage tank to a high enough temperature to kill off potentially harmful bacteria.

Medium DIY-safe £90-250

What to check first

  1. Check that your hot water timer is set to be on for at least one hour
  2. Ensure your cylinder thermostat is set to at least 60°C
  3. Check if the boiler was turned off or in standby during its scheduled disinfection cycle

Parts commonly replaced

  • Cylinder thermostat
  • NTC thermistor
  • Immersion heater backup
Full explanation for 127
128

Your boiler started to heat up but the flame went out unexpectedly while it was running.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like your hob, are working to ensure gas supply
  2. Check if your gas meter has credit
  3. Reset the boiler using the selector switch or reset button

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 128
133

Your boiler has tried to light several times but has been unable to successfully create a flame to start heating your home.

High DIY-safe £120-350

What to check first

  1. Check that your gas prepayment meter has credit
  2. Ensure other gas appliances (like a hob) are working to confirm gas supply
  3. Press the Reset button on the front of the boiler

Parts commonly replaced

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

Related codes

Full explanation for 133
153

Your boiler has been manually reset but the control board has detected a persistent internal error that prevents it from restarting safely.

High Engineer only £180-350

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for 153
160

Your boiler has stopped working because the fan that clears out exhaust gases is not running at the correct speed or has failed.

High Engineer only £220-450

Parts commonly replaced

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

Related codes

Full explanation for 160
Showing 31–40 of 129
162

Your boiler has detected an issue with the way air and exhaust fumes are moving through the system, preventing it from lighting safely.

High Engineer only £120-280

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Venture Tubes

Related codes

Full explanation for 162
164

Your boiler has detected a problem with how water is flowing through the system or a sensor that monitors pressure is sending incorrect signals.

High Engineer only £120-250

Parts commonly replaced

  • Pressure Sensor
  • Flow Switch
  • Wiring Harness

Related codes

Full explanation for 164
166

Your boiler has stopped working because it cannot confirm that the fan is safely moving air and exhaust gases through the system.

High Engineer only £120-£280

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Silicone Tubing

Related codes

Full explanation for 166
270

Your boiler has detected that it is firing without enough water inside it, which could cause the unit to overheat.

High DIY-safe £100-350

What to check first

  1. Check your central heating pressure gauge; it should be between 1.0 and 1.5 bar.
  2. If the pressure is too low, use the external filling loop to top up the system water.
  3. Ensure all radiator valves and isolation valves are fully open to allow water to circulate.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • NTC Temperature Sensor

Related codes

Full explanation for 270
432

Your boiler has detected an electrical fault with its grounding connection, which means it cannot operate safely and has shut down as a precaution.

High Engineer only £90-180

Parts commonly replaced

  • Wiring harness
  • Main circuit board (PCB)
  • Earthing cable
Full explanation for 432
433

Your boiler has shut down because it has become dangerously hot and is protecting itself from overheating.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the pressure gauge.
  3. Once the boiler has cooled down, try pressing the reset button.

Parts commonly replaced

  • Circulating Pump
  • Overheat Thermostat
  • Heat Exchanger (Flushing required)

Related codes

Full explanation for 433
E.00 – .04

Your boiler has lost communication with its internal thermometer that monitors water coming back from the radiators, causing the system to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Wiring harness / Connector

Related codes

Full explanation for E.00 – .04
E.00 – .05

Your boiler has stopped working because it cannot communicate with the internal sensor that monitors the temperature of the water returning from your radiators.

High Engineer only £90-170

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Wiring harness
  • PCB
Full explanation for E.00 – .05
E.01 – .02

Your boiler has detected that the water coming back from your radiators is hotter than the water going out, which usually means the temperature sensors are confused or water is flowing the wrong way.

High Engineer only £90-180

Parts commonly replaced

  • Flow temperature NTC sensor
  • Return temperature NTC sensor
  • Circulation pump
Full explanation for E.01 – .02
E.01 – .04

Your boiler is repeatedly losing its flame during operation, causing it to shut down as a safety precaution.

High Engineer only £120-£350

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve
  • PCB
Full explanation for E.01 – .04
Showing 41–50 of 129
E.01 – .11

Your boiler has shut down because it is struggling to move air through the system correctly, often due to high winds outside or a mechanical fault with the internal fan.

High DIY-safe £180-350

What to check first

  1. Check the outside flue terminal for any blockages like leaves or debris
  2. If it is a very windy day, wait for the weather to calm down
  3. Perform a 'Reset' by turning the selector dial to the R position for 5 seconds

Parts commonly replaced

  • Fan assembly
  • Gas/Air unit
  • Venture tube

Related codes

Full explanation for E.01 – .11
E.01 – .12

Your boiler has stopped working because it thinks the water returning to the unit is hotter than the water leaving it, which usually indicates a circulation problem or a sensor error.

High DIY-safe £100-220

What to check first

  1. Press and hold the reset button for five seconds
  2. Ensure all radiator valves are fully open to allow water to flow
  3. Check that your pump is running and not stuck

Parts commonly replaced

  • Temperature sensors (NTC thermistors)
  • Circulation pump
  • Main PCB

Related codes

Full explanation for E.01 – .12
E.01 – .17

Your boiler has stopped working because water is not moving through the system properly or a sensor has lost its connection.

High DIY-safe £100-280

What to check first

  1. Check that your central heating valves and radiator valves are open
  2. Check the system pressure gauge and top up to 1.5 bar if it is low
  3. Press the reset button or turn the control knob to 'R' and back to 'On'

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensor
  • Wiring harness

Related codes

Full explanation for E.01 – .17
E.01 – .20

Your boiler has become too hot and has shut down as a safety precaution, likely because water isn't moving through the system properly.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system water pressure is within the green zone (typically 1.0 to 1.5 bar)
  3. Perform a reset by turning the selector knob to 'R' for five seconds and releasing

Parts commonly replaced

  • Circulation pump
  • Flue gas NTC sensor
  • Main heat exchanger (de-scaling)

Related codes

Full explanation for E.01 – .20
E.02 – .00

Your boiler has recorded that the reset button was held down or pressed, which essentially tells the system to restart its sequence.

Low DIY-safe

What to check first

  1. Wait for the boiler to complete its internal restart sequence
  2. Ensure the display returns to the normal temperature reading
  3. Do not hold the reset button for more than 5 seconds if you need to use it again
Full explanation for E.02 – .00
E.02 – .07

Your boiler has detected that there is not enough water in the central heating system to operate safely.

High DIY-safe £60-120

What to check first

  1. Locate the internal filling loop under the boiler or external valves on the pipework.
  2. Slowly open the valves until you hear water moving and the pressure gauge rises.
  3. Close both valves tightly once the needle reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for E.02 – .07
E.02 – .16

Your boiler's internal computer has suffered a serious electronic failure and can no longer communicate with the heating system.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Channel Service Unit (CSU)
Full explanation for E.02 – .16
E.02 – .17

Your boiler has lost its connection to its internal gas control system, meaning it cannot safely command the gas valve to open and heat your home.

High Engineer only £250-£580

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E.02 – .17
E.02 – .19

Your boiler's internal control settings have been disrupted, likely due to a component change or a setting error on the main circuit board.

High Engineer only £100-£250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Jumper Link
Full explanation for E.02 – .19
E.02 – .20

Your boiler's internal computer settings have been altered or are incorrectly configured, preventing the unit from starting up correctly.

High Engineer only £90-180

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Jumper Link
Full explanation for E.02 – .20
Showing 51–60 of 129
E.02 – .21

Your boiler's internal configuration settings have been altered or are mismatched, which is preventing the system from operating correctly.

Medium Engineer only £80-140

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Configurator Jumper Link
Full explanation for E.02 – .21
E.02 – .47

Your boiler is having trouble communicating with the external controls like your thermostat or timer due to a wiring issue.

High Engineer only £90-180

Parts commonly replaced

  • External wiring
  • Room thermostat
  • Smart home receiver
  • PCB
Full explanation for E.02 – .47
E.02 – .48

Your boiler is having trouble communicating with your wireless thermostat or smart home controller.

High DIY-safe £60-120

What to check first

  1. Check that your wireless thermostat or receiver has power and fresh batteries.
  2. Restart your internet router if you are using a smart heating system.
  3. Follow the manufacturer's instructions for your thermostat to re-pair it with the boiler receiver.

Parts commonly replaced

  • RF Receiver
  • Wireless Thermostat
  • Batteries

Related codes

Full explanation for E.02 – .48
E.04 – .00

Your boiler has lost its connection to the component that controls the fuel supply, meaning it cannot safely ignite to provide heat or hot water.

High Engineer only £180-£350

Parts commonly replaced

  • Gas Valve
  • Wiring Harness
  • Printed Circuit Board (PCB)
Full explanation for E.04 – .00
E.04 – .01

Your boiler's internal thermometer has stopped working correctly, meaning the system cannot tell how hot the water is and has shut down as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring harness / Connector

Related codes

Full explanation for E.04 – .01
E.04 – .02

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

High Engineer only £90-160

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring Harness
Full explanation for E.04 – .02
E.04 – .03

Your boiler has shut down because it is getting too hot too quickly, usually because water isn't moving through the pipes as it should.

High DIY-safe £150-£350

What to check first

  1. Check that your radiator valves are open
  2. Ensure the system pressure is between 1 and 1.5 bar on the gauge
  3. Check for any frozen pipes if the weather is extremely cold

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor
  • Heat Exchanger (de-sludging)
Full explanation for E.04 – .03
E.04 – .04

Your boiler has stopped working because it cannot safely monitor the temperature of the exhaust gases leaving the system.

High Engineer only £120-£220

Parts commonly replaced

  • Flue temperature sensor (NTC)
  • Wiring harness
  • Control board
Full explanation for E.04 – .04
E.04 – .05

Your boiler has detected a problem with the sensor that monitors exhaust gases and has shut down as a safety precaution.

High Engineer only £120-£200

Parts commonly replaced

  • Flue Temperature Sensor (NTC)
  • Wiring Harness
  • Main Control Board
Full explanation for E.04 – .05
E.04 – .06

Your boiler has shut down because a safety sensor detected that it is getting far too hot, likely due to a blockage or a pump failure.

High Engineer only £150-£450

Parts commonly replaced

  • Flue gas sensor
  • Circulation pump
  • Heat exchanger heat-clean
Full explanation for E.04 – .06
Showing 61–70 of 129
E.04 – .08

Your boiler has overheated or sensed a lack of water flow, causing it to shut down for safety purposes.

High DIY-safe £120-280

What to check first

  1. Check that your radiator valves are open
  2. Ensure your system water pressure is between 1 and 1.5 bar
  3. Reset the boiler using the reset button or selector switch

Parts commonly replaced

  • Circulation Pump
  • Safety Thermostat (Overheat Stat)
  • NTC Temperature Sensor
Full explanation for E.04 – .08
E.04 – .10

Your boiler is unable to ignite the gas burner to provide heating or hot water, often due to a lack of gas supply or a component failure.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances in your home, like a cooker hob, are working correctly.
  2. Ensure your gas meter has credit and the isolation valve is in the 'on' position.
  3. Press the reset button or turn the selector dial to the 'R' position for five seconds.

Parts commonly replaced

  • Ignition lead
  • Elecrode set
  • Gas valve
  • PCB
Full explanation for E.04 – .10
E.04 – .12

Your boiler detects a flame when there shouldn't be one, or the internal burner is overheating, causing the system to shut down for safety.

High Engineer only £180-450

Parts commonly replaced

  • Ionisation Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
  • Burner Insulation
Full explanation for E.04 – .12
E.04 – .13

Your boiler has detected that the internal fan, which safely clears exhaust fumes, is stuck or not spinning correctly.

High Engineer only £200-450

Parts commonly replaced

  • Fan Assembly
  • Wiring Harness
  • Main Control PCB
Full explanation for E.04 – .13
E.04 – .17

Your boiler has detected a serious internal problem with how it controls gas and air flow, causing it to shut down for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Gas/air unit
Full explanation for E.04 – .17
E0

Your boiler is struggling to read its own temperature correctly, which is stopping it from heating your water and radiators safely.

High Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness
  • Main Control Board

Related codes

Full explanation for E0
E1

Your boiler has become too hot and has shut down as a safety precaution to prevent damage.

High DIY-safe £90-250

What to check first

  1. Turn off the boiler and allow it to cool down for at least 30 minutes.
  2. Use a radiator key to bleed air from all radiators in your home.
  3. Check your boiler's pressure gauge and top it up to 1.5 bar if it has dropped.
  4. Press the reset button on the front of the boiler.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Temperature Sensor (NTC Thermistor)

Related codes

Full explanation for E1
E2

Your boiler is struggling to move water around the system effectively, which is often caused by trapped air bubbles or a blockage.

High DIY-safe £0-180

What to check first

  1. Switch off the boiler and let the radiators cool down.
  2. Use a radiator key to bleed air from all radiators, starting with the ones on the ground floor.
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped after bleeding.

Parts commonly replaced

  • Circulation pump
  • Automatic air vent
  • Flow/Return thermistors

Related codes

Full explanation for E2
E3

Your boiler's internal computer has developed a fault and can no longer control the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E3
E4

Your boiler is struggling to light correctly, which may be caused by trapped air in the system or an issue with the gas supply.

High DIY-safe £80-250

What to check first

  1. Check that your gas pre-pay meter has credit (if applicable)
  2. Bleed all radiators to remove trapped air from the system
  3. Press the reset button or turn the control knob to 'Reset' for five seconds

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Lead

Related codes

Full explanation for E4
Showing 71–80 of 129
E09

Your boiler has stopped working because it cannot communicate with the component that controls the gas flow.

High Engineer only £120-280

Parts commonly replaced

  • Gas valve wiring harness
  • Gas control valve
  • Main PCB

Related codes

Full explanation for E09
E10

Your boiler is having trouble communicating with the optional sensor located on the outside of your house that monitors weather conditions.

Low Engineer only £90-180

Parts commonly replaced

  • Outdoor weather compensation sensor
  • Sensor wiring harness

Related codes

Full explanation for E10
E12

Your boiler has stopped working because it cannot detect that water is moving through the system properly.

High DIY-safe £120-280

What to check first

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

Parts commonly replaced

  • Differential pressure switch
  • Circulating pump
  • Diaphragm membrane

Related codes

Full explanation for E12
E13

Your boiler has detected that a internal safety switch is stuck, preventing the unit from starting the central heating or hot water process safely.

High Engineer only £120-240

Parts commonly replaced

  • Differential Water Flow Switch
  • Diaphragm
  • Pump

Related codes

Full explanation for E13
E15

Your boiler's electronic control board is unable to communicate properly with the gas valve, meaning the system cannot safely light the flame.

High Engineer only £180-£350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for E15
E20

Your boiler's temperature sensor has failed or is giving an incorrect reading, meaning the system doesn't know how hot the water is and has stopped running for safety.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for E20
E28

Your boiler has detected a problem with how it releases exhaust gases or a sensor failure, causing it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Flue NTC Sensor
  • Air Pressure Switch
  • Condensate Trap

Related codes

Full explanation for E28
E40

Your boiler has lost its ability to accurately measure the temperature of the water coming back from your radiators, usually because a sensor has failed or its wiring is damaged.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Return NTC Thermistor
  • Sensor Wiring Harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E40
E50

Your boiler's hot water sensor has developed a fault, meaning the system cannot accurately monitor the temperature of the water going to your taps.

Medium Engineer only £90-160

Parts commonly replaced

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

Related codes

Full explanation for E50
E53

Your boiler is struggling to breathe properly because something is obstructing the pipe that vents exhaust gases outside, or there is a problem with the internal fan.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for E53
Showing 81–90 of 129
E54

Your boiler is struggling to detect when you turn on a hot tap, meaning you might have inconsistent or no hot water.

Medium Engineer only £120-190

Parts commonly replaced

  • DHW Flow Sensor
  • Flow Turbine
  • Wiring Harness

Related codes

Full explanation for E54
E55

Your boiler has lost its fine-tuned settings and needs to recalibrate its combustion process to ensure it is burning gas safely and efficiently.

High Engineer only £100-£250

Parts commonly replaced

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

Related codes

Full explanation for E55
E78

Your boiler is having trouble measuring the water pressure correctly, which is preventing it from running safely.

High Engineer only £130-210

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

Full explanation for E78
E83/E84/E85/E86/E87

Your boiler's internal computer has lost its connection with the main control board, meaning the system can no longer send or receive instructions to operate.

High Engineer only £180-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal wiring loom
  • Display interface
Full explanation for E83/E84/E85/E86/E87
E92

Your boiler has failed an automatic internal safety test during the startup process regarding how the gas is burning.

High Engineer only £100-350

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • PCB

Related codes

Full explanation for E92
E100

Your boiler’s internal computer has lost track of the correct time, preventing it from starting up properly.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal battery (if applicable)

Related codes

Full explanation for E100
E109

Your boiler is struggling to move water around the system effectively, which is causing it to stop running to prevent overheating.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure there is enough water pressure in the system by checking the gauge
  3. Check for any air trapped in the system and bleed your radiators

Parts commonly replaced

  • Circulation pump
  • Flow/Return temperature sensors
  • Main heat exchanger (if blocked with sludge)

Related codes

Full explanation for E109
E110

Your boiler has safety-tripped because it has become too hot, often caused by a lack of water flow or a minor blockage.

High DIY-safe £100-280

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar on the pressure gauge
  2. Ensure all radiator valves and any isolation valves are fully open
  3. Allow the boiler to cool down and then press the Reset button

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Temperature Sensor

Related codes

Full explanation for E110
E117

Your boiler has too much water in the system, causing the pressure to rise above a safe operating level.

High DIY-safe £0-120

What to check first

  1. Check that the filling loop valves are fully closed
  2. Bleed water from a radiator using a bleed key into a container
  3. Monitor the pressure gauge until it returns to between 1 and 1.5 bar
  4. Reset the boiler once the pressure is correct

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E117
E118

Your boiler has stopped working because the water pressure inside the system is too low.

High DIY-safe £0-160

What to check first

  1. Locate the metal braided filling loop underneath or near your boiler.
  2. Open the small taps on the filling loop to allow water into the system.
  3. Close the taps once the pressure gauge on the boiler reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E118
Showing 91–100 of 129
E119

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver braided hose underneath the boiler).
  2. Slowly open the valve(s) 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.

Parts commonly replaced

  • Filling loop
  • Water pressure switch
  • Expansion vessel

Related codes

Full explanation for E119
E125

Your boiler is struggling to move water through the system, which is causing it to stop running to prevent overheating.

High DIY-safe £180-450

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar on the gauge
  2. Ensure all radiator valves and the boiler's isolation valves are fully open
  3. Gently bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Central heating pump
  • Water pressure switch
  • Main heat exchanger

Related codes

Full explanation for E125
E128

Your boiler is repeatedly losing its flame during operation, which has caused it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for E128
E129

Your boiler is struggling to keep its flame lit while trying to set itself up, causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Burner

Related codes

Full explanation for E129
E130

Your boiler has sensed that the exhaust gases are getting too hot and has shut down as a safety precaution.

High Engineer only £120-250

Parts commonly replaced

  • Flue NTC sensor
  • Heat exchanger (cleaning or replacement)
  • Main PCB

Related codes

Full explanation for E130
E131

Your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety mechanism to prevent damage to the flue system.

High Engineer only £120-350

Parts commonly replaced

  • Flue thermistor
  • Heat exchanger
  • Main PCB

Related codes

Full explanation for E131
E133

Your boiler has failed to light because it either cannot get enough gas or it cannot detect the flame it has sparked.

High DIY-safe £100-£350

What to check first

  1. Check that your gas emergency control valve is in the open position
  2. If you have a prepay meter, check that you have enough credit and the meter is not locked
  3. Check if other gas appliances like your hob are working correctly
  4. Press the reset button or turn the selector switch to 'R' for five seconds

Parts commonly replaced

  • Ignition lead
  • Electrode probe
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E133
E134

Your boiler is struggling to ignite because it cannot detect a flame despite trying to open the gas valve several times in a short period.

High DIY-safe £120-350

What to check first

  1. Check that your gas prepayment meter has credit (if applicable)
  2. Ensure your external gas emergency control valve is in the 'on' position
  3. Press and hold the reset button for 5 seconds to clear the fault

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe

Related codes

Full explanation for E134
E135

Your boiler has lost its gas supply or cannot detect gas entering the system, meaning it cannot ignite to provide heating or hot water.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a cooker or hob, are working to confirm your gas supply is active.
  2. Check your gas meter to ensure you have credit if you are on a prepay meter.
  3. Try resetting the boiler by following the instructions in your manual.

Parts commonly replaced

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

Related codes

Full explanation for E135
E154

Your boiler has detected that water is circulating at an unusual temperature or speed, causing it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Circulation pump

Related codes

Full explanation for E154
Showing 101–110 of 129
E160

Your boiler has detected a problem with the fan that clears away waste gases, meaning it cannot safely start up to provide heating or hot water.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for E160
E160 / E161

Your boiler has stopped working because the fan that clears out exhaust gases isn't spinning at the correct speed or has failed to start.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for E160 / E161
E163

Your boiler has lost the ability to measure the temperature of your hot water, which means it cannot heat water safely or effectively.

High Engineer only £90-160

Parts commonly replaced

  • DHW NTC thermistor sensor
  • Wiring harness connectors

Related codes

Full explanation for E163
E164

Your boiler is having trouble measuring the water pressure correctly, which is preventing it from heating your home safely.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for E164
E167

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

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for E167
E168

Your boiler's internal computer has locked itself due to an electrical interruption or sensor glitch, preventing it from starting.

High DIY-safe £250-450

What to check first

  1. Turn the power switch for the boiler off at the wall
  2. Wait for 60 seconds
  3. Turn the power back on and press the reset button

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Surge Protector

Related codes

Full explanation for E168
E193

Your boiler has detected that water is failing to circulate through the system correctly before the burner lights.

High Engineer only £180-£450

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor
  • Main PCB

Related codes

Full explanation for E193
E270

Your boiler is overheating because water is not moving through the system properly, which has caused it to shut down to prevent damage.

High DIY-safe £180-450

What to check first

  1. Check that your central heating valves under the boiler are fully open
  2. Ensure all radiator valves (TRVs) are turned to the highest setting
  3. Bleed all radiators to remove trapped air that might be blocking water flow

Parts commonly replaced

  • Central heating pump
  • Water pressure sensor
  • Main heat exchanger (flushing service)

Related codes

Full explanation for E270
E317

Your boiler has detected an issue with the electrical power timing coming into the unit, meaning the electricity supply doesn't match what the boiler needs to operate safely.

High Engineer only £100-£350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • External Power Supply/Inverter
Full explanation for E317
E321

Your boiler is unable to read the temperature of your hot water correctly, meaning you likely have no hot water or inconsistent temperatures.

High Engineer only £90-160

Parts commonly replaced

  • Hot Water NTC Thermistor
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for E321
Showing 111–120 of 129
E384

Your boiler thinks there is a flame present when there shouldn't be, which is often caused by an electrical glitch or a faulty internal sensor.

High Engineer only £120-280

Parts commonly replaced

  • Flame sensing electrode
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for E384
E385

Your boiler is not receiving enough electrical power to run safely, likely due to an issue with your home's electricity supply or a failing internal circuit board.

High Engineer only £180-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Low voltage cable harness
  • Power supply transformer

Related codes

Full explanation for E385
E430

Your boiler is temporarily checking if there is enough water pressure in the system to operate safely.

Low DIY-safe £0-120

What to check first

  1. Check the pressure gauge on your boiler or central heating system
  2. If the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 bar
  3. Ensure all radiator valves are open and there are no visible leaks

Parts commonly replaced

  • Filling loop
  • Water pressure sensor

Related codes

Full explanation for E430
H.01 – .00

Your boiler has lost its connection to the internal gas control system, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £180-450

Parts commonly replaced

  • Gas Valve
  • Main Control Board (PCB)
  • Wiring Harness

Related codes

Full explanation for H.01 – .00
H.01 – .05

Your boiler is struggling to move water around the system properly, causing it to heat up too quickly and shut down as a safety precaution.

High DIY-safe £120-280

What to check first

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

Parts commonly replaced

  • Circulation Pump
  • Flow and Return Thermistors (NTC Sensors)
  • Main Heat Exchanger (Flushing)

Related codes

Full explanation for H.01 – .05
H.01 – .08

Your boiler is overheating or water isn't moving through the pipes quickly enough to take the heat away.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Check for any frozen external condensate pipes

Parts commonly replaced

  • Circulation pump
  • Temperature thermistor (NTC sensor)
  • Heat exchanger

Related codes

Full explanation for H.01 – .08
H.01 – .14

Your boiler has detected that the internal water is getting too hot too quickly, often because something is blocking the flow of water through the system.

High DIY-safe £100-£350

What to check first

  1. Check that your radiator valves are open and not turned to the off position
  2. Ensure your system water pressure is topped up to between 1 and 1.5 bar
  3. Press the reset button once to see if the error clears

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor (NTC thermistor)
  • Main heat exchanger (de-scaling)
Full explanation for H.01 – .14
H.01 – .18

Your boiler has stopped working because water is not moving through the system properly or a sensor has detected an incorrect temperature reading.

High DIY-safe £150-£350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the pressure gauge
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Bleed your radiators to remove any trapped air pockets
  4. Restart the boiler by pressing the reset button

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensor
  • Main Heat Exchanger (Cleaning or Replacement)

Related codes

Full explanation for H.01 – .18
H.01 – .21

Your boiler is heating up too quickly because water isn't moving through the system properly or a sensor is giving an incorrect reading.

High DIY-safe £120-280

What to check first

  1. Ensure all radiator valves are fully open
  2. Check that your boiler pressure is between 1.0 and 1.5 bar
  3. Reset the boiler to see if the temporary fault clears

Parts commonly replaced

  • DHW Temperature Sensor (NTC thermistor)
  • Circulation Pump
  • Plate Heat Exchanger
Full explanation for H.01 – .21
H.02 – .02

Your boiler's internal computer brain hasn't been programmed with the correct settings and doesn't know how to operate properly.

High Engineer only £120-400

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • PCB Configuration Plug
Full explanation for H.02 – .02
Showing 121–129 of 129
H.02 – .03

Your boiler has hit a temporary software snag where its internal settings don't match what the hardware expects.

Low DIY-safe £80-160

What to check first

  1. Turn the boiler selector switch to the 'Reset' position
  2. Wait for 5 seconds
  3. Turn the switch back to your desired heating or hot water setting

Parts commonly replaced

  • Printed Circuit Board (PCB)
Full explanation for H.02 – .03
H.02 – .04

Your boiler's computer system is confused because it is receiving mismatched or incorrect internal setting information.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Parameters Key / Human Interface Unit
Full explanation for H.02 – .04
H.02 – .06

Your boiler has detected that the water pressure is too low or is dropping due to a possible leak in the system.

High DIY-safe £100-250

What to check first

  1. Check the pressure gauge on your boiler or piping; if it is below 1 bar, it needs topping up.
  2. Locate the filling loop (usually a silver flexible hose) and slowly open the valves until the pressure reaches 1.5 bar.
  3. Check all visible radiator valves and pipework for any signs of water leaks.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
  • Automatic air vent
Full explanation for H.02 – .06
H.03 -.00

Your boiler is having trouble reading its internal temperature sensors or communicating with its controls, which is preventing it from heating up safely.

High Engineer only £90-180

Parts commonly replaced

  • NTC Thermistor
  • Flue Sensor
  • Wiring Harness
Full explanation for H.03 -.00
H.03 – .01

Your boiler's internal computer is having trouble talking to its other components, which has caused the system to stop working for safety.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for H.03 – .01
H.03 – .02

Your boiler has lost its flame while it was running, which means your heating and hot water have stopped for safety reasons.

High DIY-safe £120-£280

What to check first

  1. Check that your gas supply is turned on at the meter
  2. Check if other gas appliances, like a hob, are working correctly
  3. Press and hold the reset button for five seconds

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead
Full explanation for H.03 – .02
OFF OFF OFF

Your boiler has no power and the control panel is completely blank, meaning it cannot start the heating process.

High DIY-safe £60-250

What to check first

  1. Check that the main boiler power switch (usually a fused spur near the unit) is turned on.
  2. Inspect your home's main consumer unit to see if a circuit breaker has tripped.
  3. Check if other appliances in the house have power to rule out a local power cut.

Parts commonly replaced

  • Internal Glass Fuse
  • Printed Circuit Board (PCB)
  • External Fused Spur
Full explanation for OFF OFF OFF
ON OFF ON

Your boiler has failed to light after several attempts and has shut itself down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that your gas emergency control valve is open and your gas credit has not run out
  2. Switch the boiler off at the main electrical fused spur or wall switch
  3. Wait 10 seconds and switch it back on to trigger a reset

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for ON OFF ON
ON ON ON

Your boiler has detected an internal electrical communication problem between its main components and cannot start up safely.

High Engineer only £120-280

Parts commonly replaced

  • Wiring harness
  • Printed Circuit Board (PCB)
Full explanation for ON ON ON