Baxi Bermuda Fault codes & diagnostics

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

Regular Natural Gas 10-15 kW 1966-2003 Discontinued

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.
2 Emergency 112 High 6 Medium 9 Low
Just want the most common Baxi Bermuda 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 required temperature and has temporarily stopped firing to prevent overheating, which is a normal part of its operation.

Low DIY-safe

What to check first

  1. Check your room thermostat to see if it is set to your desired temperature
  2. Wait for the boiler to cool down naturally; it will restart automatically when heat is needed
  3. Ensure your radiator valves are open to allow heat to circulate
Full explanation for 1 green flash
1 red flash

Your boiler has detected that it is getting too hot or the water isn't moving through the system properly, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that your radiator valves are open
  2. Ensure your system water pressure is within the green zone (usually 1.0 to 1.5 bar)
  3. Perform a reset by turning the control knob to 'R' or the reset position for five seconds

Parts commonly replaced

  • NTC Temperature Sensor
  • Circulation Pump
  • Overheat Thermostat

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 unsafe operation.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are open and not blocked by furniture
  2. Ensure the system water pressure is between 1 and 1.5 bar
  3. Press the reset button or turn the control knob to 'R' for five seconds

Parts commonly replaced

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

Related codes

Full explanation for 2 red flashes
3 green flashes

Your boiler is struggling to keep its flame lit and is currently trying to fix itself automatically.

Medium DIY-safe £80-200

What to check first

  1. Monitor the boiler to see if it resets itself automatically
  2. Check that other gas appliances in the home are working correctly to ensure gas supply
  3. If the fault persists or changes to 3 red flashes, contact a Gas Safe engineer

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Burner

Related codes

Full explanation for 3 green flashes
3 red flashes

Your boiler is failing to light the burner after several attempts, which means your heating and hot water will not work.

High DIY-safe £120-280

What to check first

  1. Check that your gas prepayment meter has credit (if applicable)
  2. Ensure all external gas isolation valves are turned to the 'on' position
  3. Press and hold the reset button or turn the control knob to 'R' for five seconds

Parts commonly replaced

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

Related codes

Full explanation for 3 red flashes
4 green flashes

Your boiler is having a temporary 'conversation' issue between its internal computer parts and should fix itself automatically in a moment.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to automatically reset itself
  2. Turn the power to the boiler off and back on again at the fused spur switch
  3. Ensure no buttons on the control panel are stuck or being held down

Parts commonly replaced

  • Control Interface
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 4 green flashes
4 red flashes

Your boiler has stopped working because the fan that helps remove exhaust gases is not spinning correctly or communicating with the control board.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Air Pressure Switch
  • Main PCB

Related codes

Full explanation for 4 red flashes
5 green flashes

Your boiler has experienced a temporary electronic glitch and is currently trying to reset itself to find the correct settings.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to complete its automatic self-reset process.
  2. If the fault persists, turn the boiler off at the fused spur switch for 30 seconds and turn it back on.
  3. Ensure there are no external electrical interference sources near the unit.

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for 5 green flashes
5 red flashes

Your boiler's internal memory chip has developed a communication fault, preventing the system from running safely.

High Engineer only £180-350

Parts commonly replaced

  • Parameter Storage Unit (PSU)
  • Main 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 trying to restart itself automatically.

Low DIY-safe £0-120

What to check first

  1. Wait up to 15 minutes for the boiler to automatically reset itself
  2. Turn the power to the boiler off and back on at the fused spur switch
  3. Monitor the lights to see if the flashing pattern changes to a steady light

Parts commonly replaced

  • No parts usually required
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 6 green flashes
Showing 11–20 of 129
FLASH OFF ON

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

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves are open to allow water to flow.
  2. Ensure the system water pressure is correct (usually between 1.0 and 1.5 bar).
  3. Press the reset button on the control panel once the unit has cooled down.

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Thermistor (NTC sensor)

Related codes

Full explanation for FLASH OFF ON
FLASH ON FLASH

Your boiler's electronic control centre has developed an internal fault and is no longer able to communicate with the rest of the system.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for FLASH ON FLASH
FLASH ON ON

Your boiler’s internal control board has developed an electrical fault and can no longer communicate with the rest of the unit.

High Engineer only £240-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Box

Related codes

Full explanation for FLASH ON ON
ON FLASH FLASH

Your boiler has likely run out of water or the water isn't moving around the system correctly, causing it to overheat.

High DIY-safe £100-£350

What to check first

  1. Check the system pressure gauge and top up the water if it is below 1.0 bar
  2. Ensure all radiator valves are open and not stuck shut
  3. Press the reset button to see if the fault clears

Parts commonly replaced

  • Circulating pump
  • Water pressure switch
  • Primary heat exchanger

Related codes

Full explanation for ON FLASH FLASH
ON FLASH ON

Your boiler has detected a problem with its internal temperature sensor, meaning it cannot accurately tell how hot the water is and has stopped working as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • NTC Thermistor
  • Sensor Wiring Harness

Related codes

Full explanation for ON FLASH ON
ON OFF FLASH

Your boiler has detected that the electrical wiring coming into the unit is connected backwards, which is a safety issue that prevents it from starting.

High Engineer only £80-130

Parts commonly replaced

  • Main isolation switch
  • External wiring terminals

Related codes

Full explanation for ON OFF FLASH
ON ON FLASH

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)
  • Wiring Harness

Related codes

Full explanation for ON ON FLASH
Digital codes
110

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

High DIY-safe £80-250

What to check first

  1. Turn off the boiler and allow it to cool down completely
  2. Check all radiator valves are open and bleed any trapped air from your radiators
  3. Check the system pressure gauge and top up to 1.5 bar if it is low
  4. Press the reset button on the boiler control panel

Parts commonly replaced

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

Related codes

Full explanation for 110
117

Your boiler has stopped working because there is too much water pressure in the system, which puts added stress on internal components.

High DIY-safe £0-120

What to check first

  1. Check that the filling loop valves are tightly closed
  2. Bleed water from a radiator using a bleed key to reduce pressure
  3. Monitor the pressure gauge to ensure it returns to between 1.0 and 1.5 bar
  4. Reset the boiler once the correct pressure is reached

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel

Related codes

Full explanation for 117
118

Your boiler has detected that the water pressure in the system is too low for it to operate safely and effectively.

High DIY-safe £0-160

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose with two small valves.
  2. Slowly open both valves one at a time until you hear water flowing into the system.
  3. Watch the pressure gauge and close both valves tightly once the needle reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for 118
119

Your boiler has stopped working because the water pressure in the system has dropped below the level required for it to run safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose with two small valves.
  2. Slowly open both valves to allow fresh water into the system while watching the pressure gauge.
  3. Close both valves firmly once the gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop hose
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for 119
125

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

High DIY-safe £150-£350

What to check first

  1. Check that the boiler pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves and the isolation valves under the boiler are fully open
  3. Bleed all radiators to remove trapped air pockets

Parts commonly replaced

  • Circulation pump
  • Pump cable
  • Water pressure sensor

Related codes

Full explanation for 125
127

Your boiler hasn't been able to heat the water to a high enough temperature to kill off potentially harmful bacteria in the system.

Medium Engineer only £90-250

Parts commonly replaced

  • Immersion heater
  • NTC thermistor sensor
  • Expansion vessel
  • Internal wiring loom

Related codes

Full explanation for 127
128

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

High Engineer only £120-£350

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • PCB
  • Condensate trap

Related codes

Full explanation for 128
133

Your boiler has tried to light several times but has been unable to stay on, often due to a lack of gas supply or a dirty sensor.

High DIY-safe £100-£250

What to check first

  1. Check that your gas pre-payment meter (if applicable) has enough credit.
  2. Verify that other gas appliances, like a cooker hob, are working correctly to ensure gas is reaching the property.
  3. Gently press the 'Reset' button on the boiler control panel for several seconds.

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for 133
153

Your boiler has gone into a safety lockout mode and needs to be manually restarted to check if the error clears.

High DIY-safe £0-120

What to check first

  1. Locate the reset button or selector switch on the front control panel.
  2. Press and hold the reset button for at least 5 seconds, then release it.
  3. Wait for the boiler to complete its start-up sequence to see if the fault clears.

Parts commonly replaced

  • None (Reset only)
  • PCB (if fault persists)
Full explanation for 153
160

Your boiler's fan is not spinning at the correct speed, meaning the system cannot safely clear away waste gases to start the burner.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Main PCB
  • Wiring harness

Related codes

Full explanation for 160
Showing 31–40 of 129
162

Your boiler's safety system cannot confirm that the fan is moving air correctly through the flue, preventing the boiler from lighting for safety.

High Engineer only £120-280

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Venturi Tube

Related codes

Full explanation for 162
164

Your boiler is having trouble detecting the flow of water through the system, which is preventing it from heating up correctly.

High Engineer only £120-250

Parts commonly replaced

  • Flow Switch
  • Water Pressure Sensor
  • Pump

Related codes

Full explanation for 164
166

Your boiler has detected a problem with how it moves air and exhaust gases through the system, causing it to shut down for safety.

High Engineer only £120-£250

Parts commonly replaced

  • Air Pressure Switch
  • Venturi Tube
  • Fan
  • Flue

Related codes

Full explanation for 166
270

Your boiler has detected that it is heating up much too quickly, which usually means there is not enough water moving through the system to carry the heat away safely.

High DIY-safe £100-£350

What to check first

  1. Check your boiler pressure gauge and top it up to 1.5 bar if it is too low
  2. Ensure all radiator valves are fully open to allow water to flow
  3. Check for any visible leaks around your radiators or pipework
  4. Try resetting the boiler once the pressure is corrected

Parts commonly replaced

  • Circulating Pump
  • Overheat Thermostat
  • Flow and Return Sensors

Related codes

Full explanation for 270
432

Your boiler has lost its electrical safety grounding, which is a serious electrical fault that requires immediate professional attention.

Emergency Engineer only £90-180

Parts commonly replaced

  • Main PCB
  • Wiring Harness
  • Earth Bonding Cable

Related codes

Full explanation for 432
433

Your boiler has shut down because it has become dangerously hot and is unable to cool itself down.

High DIY-safe £150-£450

What to check first

  1. Ensure all radiator valves are fully open to allow water to flow
  2. Check that the system pressure is between 1.0 and 1.5 bar
  3. Press the reset button only once the unit has cooled down

Parts commonly replaced

  • Circulation pump
  • Temperature sensors (NTC thermistors)
  • Main heat exchanger

Related codes

Full explanation for 433
E.00 – .04

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

High Engineer only £90-160

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Sensor wiring harness
Full explanation for E.00 – .04
E.00 – .05

Your boiler has lost connection with its internal sensor that monitors the temperature of the water returning to the unit, which has caused it to stop working as a safety precaution.

High Engineer only £90-190

Parts commonly replaced

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

Your boiler is confused because the water coming back from your radiators seems hotter than the water being sent out, suggesting a circulation problem or a sensor glitch.

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 struggling to keep the flame lit while it is running, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that your gas meter has credit and the isolation valve is fully open.
  2. Inspect the condensate pipe (the white plastic pipe outside) for blockages or ice.
  3. Press and hold the reset button for five seconds to restart the system.

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for E.01 – .04
Showing 41–50 of 129
E.01 – .11

Your boiler's fan is not spinning at the correct speed to safely clear waste gases, likely due to a mechanical fault or strong winds blowing down the flue.

High Engineer only £180-450

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Gas/air unit PCB

Related codes

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

Your boiler has detected that water is flowing in the wrong direction or the sensors are confused, causing it to shut down for safety.

High DIY-safe £90-220

What to check first

  1. Locate the reset button or selector switch on the front control panel.
  2. Turn the switch to the 'R' position or press the reset button for five seconds.
  3. Check that your radiator valves are open to ensure water can move freely through the system.

Parts commonly replaced

  • Return NTC thermistor sensor
  • Flow NTC thermistor sensor
  • Water pump
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 vital internal sensor has lost its connection.

High DIY-safe £90-250

What to check first

  1. Press and hold the reset button for five seconds
  2. Check that all radiator valves are open
  3. Check that the system pressure is between 1.0 and 1.5 bar on the gauge

Parts commonly replaced

  • Temperature sensor (NTC thermistor)
  • Circulation pump
  • Wiring harness

Related codes

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

Your boiler has shut down because it is getting too hot inside, likely due to a blockage in the chimney or water not moving through the system properly.

High DIY-safe £120-350

What to check first

  1. Check that the radiator valves and the main boiler valves are fully open
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the gauge
  3. Gently bleed air from your radiators using a radiator key

Parts commonly replaced

  • Flue gas NTC sensor
  • Circulation pump
  • Heat exchanger
Full explanation for E.01 – .20
E.02 – .00

Your boiler is simply letting you know that the reset button was held down or pressed recently.

Low DIY-safe

What to check first

  1. Check if the boiler resumes normal operation automatically.
  2. If the code remains, press the reset button once more to clear the display.
  3. Ensure no objects are leaning against the control panel pressing the button.
Full explanation for E.02 – .00
E.02 – .07

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 a silver braided hose with small valves under or near the boiler).
  2. Slowly open the valve(s) until you hear water flowing and watch the pressure gauge.
  3. Close the valves tightly once the pressure gauge reaches 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • 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 system's control unit.

High Engineer only £250-£450

Parts commonly replaced

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

Your boiler's internal computer has lost contact with the gas control system, preventing the unit from lighting safely.

High Engineer only £180-£450

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 computer chip has been set incorrectly or a setting has been moved, causing the control system to become confused.

High Engineer only £90-180

Parts commonly replaced

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

Your boiler's internal computer settings have been changed or misconfigured, meaning it doesn't recognize how it should be operating.

High Engineer only £80-160

Parts commonly replaced

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

Your boiler's electronic settings have been altered, causing a communication error with the main control board.

High Engineer only £90-180

Parts commonly replaced

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

Your boiler is having trouble communicating with an external control, such as your thermostat or programmer, due to a connection or wiring issue.

High Engineer only £90-180

Parts commonly replaced

  • External wiring harness
  • Wall-mounted thermostat
  • Receiver box
Full explanation for E.02 – .47
E.02 – .48

Your boiler is having trouble communicating with your wireless thermostat or external control unit.

High DIY-safe £60-180

What to check first

  1. Check that your wireless thermostat or receiver has power/new batteries
  2. Move the thermostat closer to the boiler to check for signal interference
  3. Follow the manufacturer's manual to re-pair the device to the boiler

Parts commonly replaced

  • Batteries
  • Wireless Receiver
  • Room Thermostat
Full explanation for E.02 – .48
E.04 – .00

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

High Engineer only £180-£350

Parts commonly replaced

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

Related codes

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

Your boiler has stopped working because it can no longer 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 reached an unsafe temperature because the water is not moving through the system properly.

High DIY-safe £150-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1 and 1.5 bar on the gauge
  3. Try to reset the boiler by following the instructions in your manual

Parts commonly replaced

  • Circulating Pump
  • Flow Temperature Sensor (NTC)
  • Main Heat Exchanger
Full explanation for E.04 – .03
E.04 – .04

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

High Engineer only £120-£220

Parts commonly replaced

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

Your boiler has detected a problem with the sensor that monitors exhaust gases, causing the system to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

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

Your boiler has shut down because it is getting too hot inside, which could be caused by a blockage, a pump failure, or a faulty sensor.

High Engineer only £120-350

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensor
  • Heat Exchanger
Full explanation for E.04 – .06
Showing 61–70 of 129
E.04 – .08

Your boiler has reached an unsafe temperature and has locked itself out to prevent damage, or a critical sensor has stopped working correctly.

High Engineer only £120-280

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Temperature Sensor
  • Wiring Harness
Full explanation for E.04 – .08
E.04 – .10

Your boiler has tried to start several times but cannot light the gas flame needed to heat your home.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, like a hob, are working to confirm your gas supply is active.
  2. If you have a prepaid gas meter, check that it has sufficient credit.
  3. Press and hold the reset button for five seconds to see if the boiler restarts.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensing cable
Full explanation for E.04 – .10
E.04 – .12

Your boiler has detected a flame when there shouldn't be one or the burner is becoming too hot, causing the system to shut down for safety.

High Engineer only £150-£450

Parts commonly replaced

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

Your boiler has stopped working because the fan that removes waste gases is stuck or cannot spin properly.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)
Full explanation for E.04 – .13
E.04 – .17

Your boiler has detected a serious internal problem with its fuel delivery system or airflow, which is preventing it from safely igniting.

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's internal thermometer has stopped working correctly, so the system is shutting down because it cannot accurately measure how hot the water is.

High Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness

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 £80-220

What to check first

  1. Turn off the boiler and allow it to cool down completely.
  2. Use a radiator key to bleed any trapped air from all radiators in your home.
  3. Check your system pressure gauge and top it up to 1.5 bar if it has dropped.
  4. Reset the boiler using the selector switch or reset button.

Parts commonly replaced

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

Related codes

Full explanation for E1
E2

Your boiler is struggling to move water through the system, which usually means there is trapped air or a blockage stopping the heat from reaching your radiators.

High DIY-safe £80-250

What to check first

  1. Switch off the boiler and allow the radiators to cool down
  2. Use a radiator key to bleed any trapped air from all radiators in the house
  3. Check the boiler pressure gauge and top it up to between 1.0 and 1.5 bar if it has dropped
  4. Restart the boiler to see if the fault has cleared

Parts commonly replaced

  • Central heating pump
  • Automatic air vent
  • System filter (cleaning)

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 £280-500

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E3
E4

Your boiler is struggling to light its flame, which could be caused by air trapped in your heating system.

High DIY-safe £100-280

What to check first

  1. Check if your gas supply is turned on and other gas appliances are working
  2. Switch the boiler off and then back on to reset it
  3. Follow the manufacturer's instructions to bleed your radiators to remove trapped air

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Spark generator

Related codes

Full explanation for E4
Showing 71–80 of 129
E09

Your boiler has lost its electronic connection to the gas control unit, meaning it cannot safely ignite to provide heat or hot water.

High Engineer only £120-280

Parts commonly replaced

  • Gas valve wiring harness
  • Gas valve
  • Main PCB
Full explanation for E09
E10

Your boiler is having trouble communicating with the sensor that measures the temperature outside, which helps it decide how hard to work.

Low Engineer only £90-180

Parts commonly replaced

  • Outdoor temperature sensor
  • External wiring/cabling

Related codes

Full explanation for E10
E12

Your boiler has detected that water isn't moving through the system correctly, which is preventing it from firing up for your heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Water pressure switch
  • Circulation pump
  • Flow sensor diaphragm

Related codes

Full explanation for E12
E13

Your boiler has detected that a internal water flow sensor is stuck in the 'on' position even when the pump is off, preventing the system from starting safely.

High Engineer only £120-£250

Parts commonly replaced

  • Differential water flow switch
  • Diaphragm
  • Circulation pump

Related codes

Full explanation for E13
E15

Your boiler's electronic control board is struggling to communicate with the internal gas valve, causing the system to shut down for safety.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for E15
E20

Your boiler's temperature sensor for the heating system has developed a fault or is sending an incorrect reading, meaning the unit won't know when to turn the heat on or off.

High Engineer only £90-160

Parts commonly replaced

  • Central heating NTC thermistor
  • Connecting wiring harness

Related codes

Full explanation for E20
E28

Your boiler has detected a problem with how it is getting rid of exhaust gases or a fault with its internal sensors.

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 detected a problem with the sensor that monitors the temperature of the water returning from your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Return NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for E40
E50

Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning your taps may stay cold.

High Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC thermistor
  • Wiring harness
  • Control board

Related codes

Full explanation for E50
E53

Your boiler is struggling to breathe properly because the exhaust pipe might be obstructed or the gas is not burning correctly.

Emergency Engineer only £100-250

Parts commonly replaced

  • Flue terminal
  • Gas valve
  • Seals and gaskets

Related codes

Full explanation for E53
Showing 81–90 of 129
E54

Your boiler is having trouble detecting when you turn on your taps, which means your hot water may be cold or inconsistent.

Medium Engineer only £120-190

Parts commonly replaced

  • DHW Flow Sensor
  • Wiring Harness
  • Flow Turbine

Related codes

Full explanation for E54
E55

Your boiler has lost its settings and needs to be professionally synchronised to ensure the gas is burning correctly and efficiently.

High Engineer only £90-180

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E55
E78

Your boiler has lost its ability to accurately measure the water pressure inside the system, meaning it has stopped working for safety reasons.

High Engineer only £140-£210

Parts commonly replaced

  • Water Pressure Sensor
  • Sensor Wiring Harness

Related codes

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

Your boiler’s internal computer and wiring have lost the ability to talk to each other, preventing the system from heating your home.

High Engineer only £180-450

Parts commonly replaced

  • Wiring Harness
  • Printed Circuit Board (PCB)
  • External Controller
Full explanation for E83/E84/E85/E86/E87
E92

Your boiler has detected an issue with the air and gas mix while trying to automatically calibrate itself, causing it to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Gas valve
  • Flame sensing electrode
  • Flue system components
  • PCB

Related codes

Full explanation for E92
E100

Your boiler's internal computer has lost track of the correct time, preventing it from following its programmed heating schedule.

Low DIY-safe £0-120

What to check first

  1. Locate the control panel on your boiler or wall thermostat.
  2. Access the time/date settings menu.
  3. Update the current time and date to the correct values and save the settings.
  4. Perform a reset by pressing the 'Reset' button if the error persists.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Interface unit

Related codes

Full explanation for E100
E109

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

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Bleed all radiators to remove trapped air from the system

Parts commonly replaced

  • Central heating pump
  • Flow and return thermistors
  • Main heat exchanger

Related codes

Full explanation for E109
E110

Your boiler has shut down because it has detected it is getting too hot, usually due to a lack of water flow or a circulation problem.

High DIY-safe £100-£350

What to check first

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

Parts commonly replaced

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

Related codes

Full explanation for E110
E117

Your boiler has switched off because there is too much water pressure in the system, which is usually caused by overfilling or a recent radiator top-up.

High DIY-safe £0-120

What to check first

  1. Locate a radiator bleed valve (usually at the top corner of a radiator).
  2. Use a radiator key to slowly open the valve and drain a small amount of water into a jug.
  3. Monitor the boiler pressure gauge until it falls back into the green zone (typically 1.0 to 1.5 bar) and then reset the boiler.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve (PRV)

Related codes

Full explanation for E117
E118

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 small tap handles) underneath or near the boiler.
  2. Slowly open both taps until you hear water entering the system.
  3. Watch the pressure gauge and close the taps firmly once it reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

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 £0-160

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose with two small taps.
  2. Slowly open both taps to let fresh water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both taps tightly and press the reset button on the boiler control panel.

Parts commonly replaced

  • Water pressure switch
  • Filling loop valve
  • Expansion vessel

Related codes

Full explanation for E119
E125

Your boiler is struggling to move water around the system correctly, which is causing it to shut down to prevent overheating.

High DIY-safe £180-350

What to check first

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

Parts commonly replaced

  • Circulation pump
  • System diverter valve
  • Flow temperature sensor

Related codes

Full explanation for E125
E128

Your boiler is repeatedly struggling to keep the flame lit during operation, causing it to shut down for safety.

High Engineer only £100-£350

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas Valve
  • PCB

Related codes

Full explanation for E128
E129

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

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Burner
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E129
E130

Your boiler has detected that the exhaust gases are getting too hot, so it has shut down as a safety precaution.

High Engineer only £120-220

Parts commonly replaced

  • Flue NTC Sensor
  • Heat Exchanger cleaning
  • Main PCB

Related codes

Full explanation for E130
E131

Your boiler has shut down because it has detected that the exhaust gases are becoming dangerously hot, which has triggered a safety lockout.

High Engineer only £120-350

Parts commonly replaced

  • Flue Overheat Thermostat
  • Heat Exchanger cleaning service
  • Main PCB

Related codes

Full explanation for E131
E133

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

High DIY-safe £100-£350

What to check first

  1. Check that your gas emergency control valve and any appliance isolation valves are fully open.
  2. If you have a pre-payment meter, ensure you have sufficient credit and the meter hasn't 'locked out'.
  3. Press the reset button on the fascia for five seconds to see if the boiler restarts.

Parts commonly replaced

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

Related codes

Full explanation for E133
E134

Your boiler has failed to ignite after several attempts and has locked itself out for safety.

High DIY-safe £100-£250

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your meter
  2. Press and hold the reset button for five seconds
  3. Ensure other gas appliances in the home, like a hob, are working correctly to confirm gas supply

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensing cable

Related codes

Full explanation for E134
E135

Your boiler has stopped working because it cannot detect a steady flow of gas, likely due to a communication fault between the internal controls and the gas valve.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for E135
E154

Your boiler has detected that water is circulating at an unusual temperature, suggesting a potential blockage or a failing internal pump.

High Engineer only £150-350

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor
  • Return Temperature Sensor

Related codes

Full explanation for E154
Showing 101–110 of 129
E160

Your boiler has detected a problem with the fan that clears out exhaust gases, meaning the system has shut down as a safety precaution.

High Engineer only £250-£450

Parts commonly replaced

  • Extraction fan
  • Fan wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E160
E160 / E161

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

High Engineer only £220-£450

Parts commonly replaced

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

Related codes

Full explanation for E160 / E161
E163

Your boiler's temperature sensor for hot water has stopped working correctly, meaning your taps may not get warm even if the heating is running.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW NTC thermistor sensor
  • Wiring harness connector

Related codes

Full explanation for E163
E164

Your boiler's internal computer is struggling to read the water pressure correctly, meaning it cannot confirm if it is safe to operate.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure sensor
  • Pressure switch
  • Wiring harness

Related codes

Full explanation for E164
E167

Your boiler's internal computer has encountered a communication error or technical failure, preventing the system from running safely.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E167
E168

Your boiler's internal computer has encountered a memory or logic error and has shut itself down as a safety precaution.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • External surge protector

Related codes

Full explanation for E168
E193

Your boiler has detected that water is not circulating properly before the burner ignites, which may be caused by an air lock or a blockage.

High DIY-safe £120-350

What to check first

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

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor
  • Automatic air vent

Related codes

Full explanation for E193
E270

Your boiler has detected that water isn't moving through the system properly, which is causing it to overheat too quickly.

High DIY-safe £150-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system pressure is between 1 and 1.5 bar on the gauge
  3. Gently bleed your radiators to remove any trapped air
  4. Reset the boiler to see if the fault clears

Parts commonly replaced

  • Circulation pump
  • Primary temperature sensor
  • Heat exchanger

Related codes

Full explanation for E270
E317

Your boiler has detected an issue with the electrical power supply frequency, meaning it isn't receiving the steady electrical signal it needs to operate safely.

High Engineer only £150-450

Parts commonly replaced

  • Main PCB
  • External Voltage Regulator
Full explanation for E317
E321

Your boiler is struggling to accurately measure the temperature of your hot water, which usually means a sensor has failed.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC thermistor
  • Connecting wiring harness

Related codes

Full explanation for E321
Showing 111–120 of 129
E384

Your boiler thinks there is a flame burning even when there shouldn't be, which is a safety conflict that prevents it from starting up.

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 operate correctly, causing it to shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check if there is a power cut or 'brownout' in your local area.
  2. Ensure your fuse box hasn't tripped and that the boiler's fused spur is switched on.
  3. Turn the boiler power off at the wall for 30 seconds and then switch it back on to reset the electronics.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External power supply cable
  • Voltage protector/regulator

Related codes

Full explanation for E385
E430

Your boiler is temporarily checking the water pressure levels and has paused operation to ensure there is enough water in the system.

Low DIY-safe £0-80

What to check first

  1. Check the pressure gauge on your boiler or expansion vessel.
  2. If the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 bar.
  3. Restart the boiler to clear the temporary test message.

Parts commonly replaced

  • Filling loop
  • Pressure sensor

Related codes

Full explanation for E430
H.01 – .00

Your boiler has lost its connection with 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
  • Printed Circuit Board (PCB)
  • Wiring loom

Related codes

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

Your boiler is overheating because water isn't moving through the system quickly enough or the temperature sensors are giving incorrect readings.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system pressure is between 1 and 1.5 bar on the gauge
  3. Try bleeding your radiators to remove trapped air

Parts commonly replaced

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

Related codes

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

Your boiler is heating up too quickly because water isn't moving through the system properly, causing it to shut down to prevent overheating.

High DIY-safe £120-300

What to check first

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

Parts commonly replaced

  • Circulation Pump
  • Temperature Sensor (NTC Thermistor)
  • Flow/Return Thermistor

Related codes

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

Your boiler has detected that it is getting too hot too quickly, likely because the water is not moving through the system as fast as it should.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves (TRVs) are fully open to allow water flow.
  2. Ensure that the water pressure on the boiler's gauge is between 1 and 1.5 bar.
  3. Bleed all radiators to remove trapped air that could be blocking circulation.

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor (NTC thermistor)
  • Main heat exchanger
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 £120-350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure the central heating pump is running and not stuck
  3. Check that your system water pressure is within the normal range (usually 1.0 to 1.5 bar)

Parts commonly replaced

  • Circulation Pump
  • Flow/Return Temperature Sensor
  • Main Heat Exchanger (if blocked)

Related codes

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

Your boiler is heating up too quickly when you turn the tap on, which is causing it to shut down for safety.

High Engineer only £120-300

Parts commonly replaced

  • Domestic Hot Water Temperature Sensor
  • Plate Heat Exchanger
  • Circulation Pump
Full explanation for H.01 – .21
H.02 – .02

Your boiler's internal computer brain hasn't been set up correctly or has lost its memory, so it doesn't know how to operate.

High Engineer only £120-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Parameter Key

Related codes

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 have become confused and it may need a reset or its configuration checked by a professional.

Low DIY-safe £80-160

What to check first

  1. Locate the reset button on the control panel
  2. Press and hold the reset button for five seconds
  3. Wait for the boiler to restart and monitor if the code clears

Parts commonly replaced

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

Your boiler's computer system has encountered a temporary settings error and is struggling to communicate with its internal components correctly.

Medium DIY-safe £90-250

What to check first

  1. Locate the reset button or dial on the front control panel.
  2. Press and hold the reset button for five seconds, then release.
  3. Wait for the boiler to restart and monitor the display for the error to clear.

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Parameter key

Related codes

Full explanation for H.02 – .04
H.02 – .06

Your boiler has detected that the water pressure is too low or unstable, often due to a leak or the system needing to be topped up.

High DIY-safe £80-250

What to check first

  1. Check the pressure gauge on your boiler or expansion vessel
  2. If the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 bar
  3. Check all visible radiator valves and pipework for signs of a water leak
  4. Restart the boiler to see if the code clears

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
  • Pressure sensor

Related codes

Full explanation for H.02 – .06
H.03 -.00

Your boiler is struggling to read its sensors correctly, which has caused it to stop running as a safety precaution.

High Engineer only £90-180

Parts commonly replaced

  • NTC Temperature Sensor
  • Flue Sensor
  • Wiring Harness

Related codes

Full explanation for H.03 -.00
H.03 – .01

Your boiler's internal computer is having trouble communicating with the main control system, meaning the unit cannot start up or operate correctly.

High Engineer only £280-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Communication Cable Harness

Related codes

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

Your boiler has lost its flame while running and has shut down for safety, meaning you won't have any heating or hot water until it is fixed.

High Engineer only £120-300

Parts commonly replaced

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

Related codes

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

Your boiler is not receiving any electricity, which means the display and all heating functions have completely shut down.

High DIY-safe £0-120

What to check first

  1. Check if your home has had a power cut
  2. Ensure the boiler's fused spur switch is turned on
  3. Check your main consumer unit (fuse box) to see if a circuit breaker has tripped
  4. Replace the 3-amp fuse in the boiler's power switch

Parts commonly replaced

  • 3-amp fuse
  • PCB (Printed Circuit Board)
  • Wiring harness
Full explanation for OFF OFF OFF
ON OFF ON

Your boiler has tried to light several times but has failed to stay on, meaning your heating and hot water will not work.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances in your home, like a cooker, are working to ensure gas supply.
  2. Ensure your prepaid gas meter has credit if applicable.
  3. Switch the boiler off and back on to attempt a reset.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe

Related codes

Full explanation for ON OFF ON
ON ON ON

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

High Engineer only £120-£250

Parts commonly replaced

  • Wiring harness
  • PCB (Printed Circuit Board)
  • Low voltage cable assembly

Related codes

Full explanation for ON ON ON