Baxi Suprima 30 Fault codes & diagnostics

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

Regular Natural Gas 8.8 kW 1998-2010 Discontinued

Replaced by: Potterton Promax HE

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.
117 High 6 Medium 6 Low
Just want the most common Baxi Suprima 30 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 pausing until the water cools down enough to start heating again.

Low DIY-safe

What to check first

  1. No action is needed as this is normal operation.
  2. If you want the room warmer, check your room thermostat is turned up.
  3. Ensure your radiator valves are open if you feel the house is still cold.
Full explanation for 1 green flash
1 red flash

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

High DIY-safe £120-280

What to check first

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

Parts commonly replaced

  • Temperature Sensor (Thermistor)
  • Circulation Pump
  • PCB (Control Board)

Related codes

Full explanation for 1 red flash
2 red flashes

Your boiler has become too hot and has automatically shut down for safety purposes.

High DIY-safe £120-350

What to check first

  1. Wait for the boiler to cool down for at least 20 minutes
  2. Check that all radiator valves are open and not blocked by furniture
  3. Press the 'Reset' button on the front control panel
  4. Check if the pressure gauge is at least 1 bar (if a system boiler)

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • PCB (Control Board)
  • Thermistor

Related codes

Full explanation for 2 red flashes
3 green flashes

Your boiler has temporarily lost its flame and is attempting to restart its sequence automatically.

Medium Engineer only £120-350

Parts commonly replaced

  • Flame sense electrode
  • Ignition lead
  • PCB (Control Board)

Related codes

Full explanation for 3 green flashes
3 red flashes

Your boiler is failing to light its internal flame after several attempts, meaning your heating and hot water will not work.

High DIY-safe £120-350

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Check if other gas appliances like a hob are working to confirm gas supply
  3. Press the 'Reset' button firmly for two seconds and wait for the boiler to restart

Parts commonly replaced

  • PCB (Control Board)
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for 3 red flashes
4 green flashes

Your boiler is experiencing a brief communication hiccup between its internal electronic parts and should correct itself automatically.

Low DIY-safe £0-280

What to check first

  1. Monitor the boiler for a few minutes as it should self-reset
  2. If the error persists, turn the control knob to the 'Reset' position for 5 seconds
  3. Ensure any external controls or thermostats are calling for heat

Parts commonly replaced

  • Main PCB
  • Control Knob/Interface Board
Full explanation for 4 green flashes
4 red flashes

Your boiler's internal cooling and exhaust fan is not spinning correctly, which is preventing the system from starting up for safety reasons.

High Engineer only £180-350

Parts commonly replaced

  • Fan Assembly
  • Air Pressure Switch
  • PCB (Printed Circuit Board)

Related codes

Full explanation for 4 red flashes
5 green flashes

Your boiler has experienced a brief electronic glitch in its internal computer, but it should clear itself automatically once it recalibrates.

Low DIY-safe £250-450

What to check first

  1. Wait for the boiler to automatically reset itself
  2. If the flashing continues for more than 10 minutes, turn the power switch off and back on again
  3. Observe if the fault returns regularly, as this may indicate a failing board

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Control Knob/Interface
Full explanation for 5 green flashes
5 red flashes

Your boiler’s internal computer chip has encountered a technical memory error and can no longer communicate with the main control board.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for 5 red flashes
6 green flashes

Your boiler has experienced a temporary hiccup and is currently trying to reset itself to resume normal operation.

Low DIY-safe £0-120

What to check first

  1. Wait up to 15 minutes for the boiler to automatically reset
  2. If it does not reset, press and release the reset button once
  3. Ensure there is power to the boiler and the gas supply is active

Parts commonly replaced

  • None (usually self-clearing)
  • PCB (if fault persists)
Full explanation for 6 green flashes
Showing 11–20 of 129
6 red flashes

Your boiler has encountered an internal logic error and cannot tell exactly what is wrong, which has caused it to stop working for safety.

High Engineer only £180-350

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Ignition Lead
  • Electrode Probes
Full explanation for 6 red flashes
FLASH OFF FLASH

Your boiler is not receiving enough electrical power from the mains supply to operate safely.

High Engineer only £180-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Mains transformer

Related codes

Full explanation for FLASH OFF FLASH
FLASH OFF ON

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

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are open and not blocked
  2. Allow the boiler to cool down for at least 30 minutes
  3. Press the reset button firmly for 2 to 5 seconds

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • PCB (Control Board)

Related codes

Full explanation for FLASH OFF ON
FLASH ON FLASH

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

  • Main 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 can no longer control the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • PCB Ignition Kit

Related codes

Full explanation for FLASH ON ON
ON FLASH FLASH

Your boiler has detected that water is not moving through the system properly or there is air trapped inside, causing it to overheat quickly.

High DIY-safe £100-£350

What to check first

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

Parts commonly replaced

  • Central heating pump
  • External system bypass valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ON FLASH FLASH
ON FLASH ON

Your boiler has stopped heating because a temperature sensor is reporting incorrect or faulty information to the main control board.

High Engineer only £90-180

Parts commonly replaced

  • NTC Thermistor
  • Control Board (PCB)

Related codes

Full explanation for ON FLASH ON
ON OFF FLASH

Your boiler has detected an electrical wiring issue where the power supply wires appear to be connected the wrong way around.

High Engineer only £90-180

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Wiring Junction Box
Full explanation for ON OFF FLASH
ON ON FLASH

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

High Engineer only £240-380

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Ignition Lead
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 £90-250

What to check first

  1. Turn off the boiler and allow it to cool down completely.
  2. Check and bleed all radiators using a radiator key to release trapped air.
  3. Ensure all radiator valves (TRVs) are fully open.
  4. Press the reset button on the boiler control panel once cooled.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Flow/Return Thermistors
Full explanation for 110
117

Your boiler has too much water inside it, causing the internal pressure to rise above the safe operating limit.

Medium DIY-safe £80-200

What to check first

  1. Check that the silver filling loop valves are fully closed
  2. Bleed water from a radiator using a bleed key to lower the pressure
  3. Monitor the pressure gauge until it returns to the green zone (typically 1.0 - 1.5 bar)
  4. Press the reset button if the fault code persists

Parts commonly replaced

  • Expansion Vessel
  • Filling Loop
  • Pressure Relief Valve (PRV)

Related codes

Full explanation for 117
118

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

High DIY-safe £0-160

What to check first

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

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for 118
119

Your boiler has stopped working because there is not enough water pressure in the central heating system.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.
  2. Slowly open the valve(s) to let water into the system while watching the pressure gauge.
  3. Close the valve(s) tightly once the gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel recharge

Related codes

Full explanation for 119
125

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

High DIY-safe £150-350

What to check first

  1. Check that your central heating valves and radiator valves are open
  2. Ensure your system water pressure is between 1.0 and 1.5 bar
  3. Try resetting the boiler to see if the fault clears
  4. Gently bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Central heating pump
  • Overheat thermostat
  • Automatic air vent

Related codes

Full explanation for 125
127

Your boiler has failed to heat the water in your cylinder to a high enough temperature to kill off potentially harmful bacteria.

Medium DIY-safe £90-220

What to check first

  1. Check that your hot water cylinder thermostat is set to at least 60°C
  2. Ensure your boiler control knob is not turned to the 'minimum' or 'off' position
  3. Check your programmer to ensure the hot water heating window is long enough (at least 1 hour) for the tank to reach full temperature

Parts commonly replaced

  • Cylinder Tech thermostat
  • NTC Immersion Sensor
  • PCB (Control Board)

Related codes

Full explanation for 127
128

Your boiler started up correctly but the flame went out unexpectedly while it was running, causing the system to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

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

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 the heating process.

High DIY-safe £120-£350

What to check first

  1. Check that your gas supply is turned on at the meter
  2. If you have a prepaid gas meter, check that you have sufficient credit
  3. Press and hold the reset button for five seconds

Parts commonly replaced

  • Ignition electrodes
  • Gas valve
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 133
153

Your boiler has experienced a glitch or a safety interruption and has been manually unlocked, but it may still require a full reset or professional inspection to clear the underlying issue.

High DIY-safe £100-£350

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for at least 5 seconds.
  3. Wait for the status light to change; if the fault persists or returns immediately, contact a Gas Safe engineer.

Parts commonly replaced

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

Related codes

Full explanation for 153
160

Your boiler has detected an issue with the part that clears waste gases, preventing the system from starting for your safety.

High Engineer only £250-450

Parts commonly replaced

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

Related codes

Full explanation for 160
Showing 31–40 of 129
162

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
  • Venturi Tube

Related codes

Full explanation for 162
164

Your boiler has detected an issue with how the water is circulating or how the pressure is being measured, causing it to stop running for safety.

High Engineer only £120-£250

Parts commonly replaced

  • Flow switch
  • Water pressure sensor
  • Circulation pump

Related codes

Full explanation for 164
166

Your boiler has stopped working because it cannot confirm that the fan is safely clearing waste gases from the system.

High Engineer only £120-£280

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Silicone Pressure Tubes

Related codes

Full explanation for 166
270

Your boiler has detected that it is trying to heat up without enough water flowing through it, which could cause the unit to overheat.

High DIY-safe £100-£350

What to check first

  1. Check if your system water pressure is too low and top it up using the filling loop
  2. Ensure all radiator valves are open to allow water to flow
  3. Gently bleed your radiators to remove any trapped air pockets
  4. Press the reset button once the pressure is restored

Parts commonly replaced

  • Circulating pump
  • Automatic air vent
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 270
432

Your boiler has detected an electrical safety issue where the internal wiring is not properly grounded.

High Engineer only £90-180

Parts commonly replaced

  • Wiring harness
  • PCB (Printed Circuit Board)
  • Earth lead connection

Related codes

Full explanation for 432
433

Your boiler has shut down because it has detected that the internal water temperature has become dangerously hot.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Check that the external pump (usually in the airing cupboard) is running
  3. Allow the boiler to cool down and press the reset button

Parts commonly replaced

  • External Circulation Pump
  • Overheat Thermostat
  • Temperature Sensor (NTC)
  • Printed Circuit Board (PCB)
Full explanation for 433
E.00 – .04

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

High Engineer only £100-180

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Wiring harness / Connector
Full explanation for E.00 – .04
E.00 – .05

Your boiler has detected a communication problem with the sensor that monitors water returning from your radiators, preventing it from heating up correctly.

High Engineer only £90-160

Parts commonly replaced

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

Your boiler has sensed that the water returning to it is hotter than the water leaving it, which usually means the temperature sensors have become confused or the internal water flow is incorrect.

High Engineer only £120-250

Parts commonly replaced

  • Flow/Return NTC Thermistors
  • Boiler Control PCB
  • External Pump
Full explanation for E.01 – .02
E.01 – .04

Your boiler is repeatedly struggling to keep the flame lit, causing it to shut down for safety after multiple failed attempts.

High DIY-safe £120-350

What to check first

  1. Check that your gas emergency control valve is fully open
  2. If you have a pre-payment meter, verify that you have enough credit
  3. Try resetting the boiler by pressing the reset button for five seconds

Parts commonly replaced

  • Flame rectification electrode
  • Gas valve
  • PCB (Printed Circuit Board)
Full explanation for E.01 – .04
Showing 41–50 of 129
E.01 – .11

Your boiler's fan isn't spinning at the right speed to safely clear away exhaust fumes, which has caused the system to shut down for safety.

High Engineer only £180-£350

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Main PCB
Full explanation for E.01 – .11
E.01 – .12

Your boiler has detected that the water coming back is hotter than the water going out, which usually means the water isn't circulating properly through your system.

High DIY-safe £120-280

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for at least 5 seconds.
  3. Ensure all radiator valves are open and the pump is not making unusual grinding noises.

Parts commonly replaced

  • Central heating pump
  • Return temperature sensor (NTC thermistor)
  • Flow temperature sensor
Full explanation for E.01 – .12
E.01 – .17

Your boiler has likely stopped heating because water isn't moving through the system properly or a vital sensor has lost its connection.

High DIY-safe £120-350

What to check first

  1. Press and hold the reset button for at least 5 seconds
  2. Check that all radiator valves and boiler isolation valves are fully open
  3. Ensure your system pressure is topped up to between 1 and 1.5 bar on the gauge

Parts commonly replaced

  • Temperature Sensor (Thermistor)
  • Circulation Pump
  • Control PCB
Full explanation for E.01 – .17
E.01 – .20

Your boiler has shut down because it is getting too hot, likely because water isn't flowing through the system properly or a sensor has failed.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the central heating system pressure is between 1 and 1.5 bar
  3. Press the reset button and wait for the boiler to restart

Parts commonly replaced

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

Your boiler is simply indicating that the reset button has been pressed and it is restarting itself.

Low DIY-safe

What to check first

  1. Wait for the boiler to complete its startup sequence
  2. Ensure the display returns to showing normal temperature or operation status
  3. Monitor the boiler for a few minutes to ensure it fires up correctly
Full explanation for E.02 – .00
E.02 – .07

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

High DIY-safe £0-160

What to check first

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

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure sensor
Full explanation for E.02 – .07
E.02 – .16

Your boiler's main control computer has suffered an internal failure and can no longer process its operations correctly.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness
Full explanation for E.02 – .16
E.02 – .17

Your boiler's internal computer has lost touch with the gas control system, meaning it cannot safely manage the fuel needed to generate heat.

High Engineer only £250-£550

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Gas Valve
  • Wiring Harness
Full explanation for E.02 – .17
E.02 – .19

Your boiler's main control board has detected an internal configuration error, likely caused by a component fault or an incorrect setting on the circuit board.

High Engineer only £220-380

Parts commonly replaced

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

Your boiler's internal control settings have been disrupted or a component has been incorrectly configured, preventing the system from starting up.

High Engineer only £100-250

Parts commonly replaced

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

Your boiler's main control board has detected a configuration setting error, likely caused by a technical fault or an incorrect setup during a repair.

High Engineer only £180-350

Parts commonly replaced

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

Your boiler is having trouble communicating with external controls like your thermostat or programmer because of a potential wiring problem.

High Engineer only £90-180

Parts commonly replaced

  • External control wiring
  • PCB (Printed Circuit Board)
  • Appliance Interface
Full explanation for E.02 – .47
E.02 – .48

Your boiler is having trouble 'speaking' to your thermostat or external controls, meaning they aren't working together correctly to manage your heating.

High DIY-safe £80-220

What to check first

  1. Check that your wireless thermostat or programmer has fresh batteries.
  2. Ensure the external controls are switched on and within range of the boiler.
  3. Consult your thermostat manual to perform a 're-pairing' or 're-binding' procedure with the receiver.
  4. Restart the boiler using the reset button to see if it re-establishes the connection.

Parts commonly replaced

  • Wireless thermostat
  • RF Receiver
  • Printed Circuit Board (PCB)
Full explanation for E.02 – .48
E.04 – .00

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

High Engineer only £180-350

Parts commonly replaced

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

Your boiler has lost track of the water temperature because a sensor has failed or become disconnected, causing the system to stop working for safety.

High Engineer only £90-160

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring Harness
Full explanation for E.04 – .01
E.04 – .02

Your boiler has stopped working because it cannot accurately measure the temperature of the water flowing through the system.

High Engineer only £100-£180

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring Harness
  • Control Board (PCB)

Related codes

Full explanation for E.04 – .02
E.04 – .03

Your boiler has overheated because water isn't moving through the system properly, causing it to shut down for safety.

High DIY-safe £150-350

What to check first

  1. Check that your radiator valves and any isolation valves are fully open
  2. Ensure your system pressure is topped up to between 1.0 and 1.5 bar
  3. Try bleeding your radiators to remove trapped air that could be blocking flow
  4. Reset the boiler using the reset button or dial once it has cooled down

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Flow temperature sensor
Full explanation for E.04 – .03
E.04 – .04

Your boiler has detected an issue with the sensor that monitors exhaust gases, meaning it has shut down for safety purposes.

High Engineer only £120-£220

Parts commonly replaced

  • Flue Temperature Sensor (NTC)
  • Wiring harness
  • PCB (Printed Circuit Board)
Full explanation for E.04 – .04
E.04 – .05

Your boiler has detected an issue with the sensor that monitors exhaust gases, meaning it has shut down for safety to prevent damage.

High Engineer only £120-210

Parts commonly replaced

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

Your boiler has shut down because it is becoming too hot and cannot safely move heat away from the system.

High Engineer only £120-£350

Parts commonly replaced

  • Circulation pump
  • Flue Gas Temperature Sensor (NTC)
  • Heat Exchanger cleaning
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 overheating.

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves are open to allow water to flow.
  2. Ensure your system pressure is topped up correctly (usually 1 to 1.5 bar).
  3. Press the reset button once the boiler has cooled down for 20 minutes.

Parts commonly replaced

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

Your boiler is unable to ignite its flame, meaning it cannot provide heating or hot water until the issue is resolved.

High DIY-safe £120-280

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 prepayment meter, ensure you have 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
  • Printed Circuit Board (PCB)
Full explanation for E.04 – .10
E.04 – .12

Your boiler thinks a flame is present when it should be off, or it is overheating due to an incorrect mix of gas and air.

High Engineer only £180-450

Parts commonly replaced

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

Related codes

Full explanation for E.04 – .12
E.04 – .13

Your boiler has stopped working because the fan that clears away waste gases is either stuck or not getting the power it needs to spin.

High Engineer only £220-450

Parts commonly replaced

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

Your boiler has detected a serious mechanical fault with its gas supply system or internal controls and has locked itself for safety.

High Engineer only £220-450

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Venturi Assembly
Full explanation for E.04 – .17
E0

Your boiler's internal thermometer is likely broken or disconnected, meaning the system has shut down because it cannot safely monitor its own temperature.

High Engineer only £100-£180

Parts commonly replaced

  • NTC thermistor (temperature sensor)
  • Sensor wiring harness
  • PCB

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 £100-250

What to check first

  1. Wait for the boiler to cool down completely
  2. Check that all radiator valves are open
  3. Bleed your radiators to remove any trapped air
  4. Press the reset button on the front of the boiler

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • NTC Temperature Sensor

Related codes

Full explanation for E1
E2

Your boiler is struggling to push water through the house, likely because of trapped air bubbles or a blockage in the system.

High DIY-safe £80-250

What to check first

  1. Turn off the boiler and allow the system to cool down.
  2. Use a radiator key to bleed air from all radiators, starting with the ones downstairs.
  3. Check your boiler pressure gauge and top it up to 1.5 bar if it has dropped.
  4. Restart the boiler to see if the error clears.

Parts commonly replaced

  • Circulating Pump
  • Automatic Air Vent
  • Flow/Return Thermistor

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

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E3
E4

Your boiler is struggling to light its flame, but this could be caused by air trapped in your heating system preventing proper water flow.

High DIY-safe £80-250

What to check first

  1. Locate your radiator bleed key
  2. Turn off your heating and allow the radiators to cool
  3. Open the bleed valve on each radiator until air stops hissing and water appears
  4. Reset the boiler using the reset button

Parts commonly replaced

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

Related codes

Full explanation for E4
Showing 71–80 of 129
E09

Your boiler has lost communication with its gas control unit, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £120-£350

Parts commonly replaced

  • Gas valve wiring harness
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for E09
E10

Your boiler is having trouble communicating with the optional sensor used to monitor the weather outside.

Low DIY-safe £90-180

What to check first

  1. Check if the boiler operates normally in manual mode without outdoor compensation
  2. Inspect the outdoor sensor wire for any obvious external damage or loose connections
  3. Reset the boiler to see if the communication error clears

Parts commonly replaced

  • Outdoor temperature sensor
  • Sensor wiring

Related codes

Full explanation for E10
E12

Your boiler has detected that water isn't moving through the system correctly, so it has shut down to prevent overheating.

High Engineer only £120-280

Parts commonly replaced

  • Circulating pump
  • Differential pressure switch
  • Main PCB

Related codes

Full explanation for E12
E13

Your boiler has detected that a internal water flow sensor is stuck, meaning the system cannot correctly tell if water is moving before it starts the burner.

High Engineer only £120-250

Parts commonly replaced

  • Differential pressure switch
  • Circulating pump
  • Diaphragm

Related codes

Full explanation for E13
E15

Your boiler's internal computer is having trouble communicating with the mechanism that controls the gas supply, meaning it cannot safely light or stay on.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for E15
E20

Your boiler's temperature sensor has developed a fault or is disconnected, preventing the system from knowing how hot the water is.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for E20
E28

Your boiler has detected a problem with how it disposes of waste gases or a sensor error, 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 measure the temperature of the water returning from your radiators, preventing it from heating your home safely.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Return NTC Sensor
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for E40
E50

Your boiler is having trouble measuring the temperature of your hot water because a sensor has likely failed or become disconnected.

High Engineer only £90-160

Parts commonly replaced

  • Hot water NTC sensor
  • Wiring harness

Related codes

Full explanation for E50
E53

Your boiler has detected that the exhaust gases are not clear or the air pipe might be obstructed, causing it to shut down for safety.

High Engineer only £100-£350

Parts commonly replaced

  • Fan
  • Air Pressure Switch
  • Venturi Tube
  • Gas Valve

Related codes

Full explanation for E53
Showing 81–90 of 129
E54

Your boiler is struggling to detect when you turn on your hot taps, meaning you may experience cold water or inconsistent temperatures.

High Engineer only £120-220

Parts commonly replaced

  • DHW flow sensor
  • Connecting wiring harness

Related codes

Full explanation for E54
E55

Your boiler has lost its internal settings and needs a professional engineer to electronically re-configure it to work correctly.

High Engineer only £90-180

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Interface Cable

Related codes

Full explanation for E55
E78

Your boiler is unable to accurately measure the water pressure inside the system, which is preventing it from heating your home safely.

High Engineer only £140-220

Parts commonly replaced

  • Water pressure sensor (transducer)
  • Wiring harness
  • Main PCB

Related codes

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

Your boiler's main control board has lost contact with its internal components, meaning the system cannot talk to itself to safely start up.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness
  • Display Interface Board
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, preventing it from starting up safely.

High Engineer only £120-350

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Flame Sensing Electrode
Full explanation for E92
E100

Your boiler's internal computer has lost track of the time or date, which is preventing it from running its scheduled heating cycles.

Medium DIY-safe £0-120

What to check first

  1. Locate the control panel on the front of the boiler
  2. Navigate to the time and date settings menu
  3. Correct the current time and date and save the settings
  4. Press the reset button if the error persists

Parts commonly replaced

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

Related codes

Full explanation for E100
E109

Your boiler is struggling to move heated water through the pipes, causing it to shut down to prevent overheating.

High DIY-safe £150-350

What to check first

  1. Check that your system pressure is between 1 and 1.5 bar
  2. Ensure all radiator valves and internal bypass valves are fully open
  3. Bleed all radiators to remove trapped air that might be blocking water flow

Parts commonly replaced

  • Circulation Pump
  • Flow/Return Thermistors
  • Main PCB

Related codes

Full explanation for E109
E110

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

High DIY-safe £120-280

What to check first

  1. Check if any radiator valves or the main bypass valve are closed.
  2. Ensure all radiator thermostats are turned up to encourage water flow.
  3. Wait for 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 detected that there is too much water pressure in the system, which can cause the safety valve to leak.

Medium DIY-safe £0-120

What to check first

  1. Locate the bleed valve on a radiator (usually a small square pin).
  2. Use a radiator key and a cloth to slowly open the valve and release a small amount of water into a container.
  3. Check the boiler pressure gauge frequently to ensure it returns to the normal green zone, typically between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E117
E118

Your boiler has stopped working because there is not enough water pressure in the central heating system.

High DIY-safe £0-160

What to check first

  1. Locate the external filling loop (the silver flexible hose) usually found under the boiler or near the hot water cylinder.
  2. Slowly open the one or two taps on the loop until you hear water flowing and the pressure gauge rises.
  3. Close the taps firmly once the gauge reaches between 1.0 and 1.5 bar, then press the reset button if the error persists.

Parts commonly replaced

  • External 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 underneath the boiler.
  2. Slowly open the valves until you hear water moving and watch the pressure gauge.
  3. Close the valves tightly once the gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • External Filling Loop
  • Water Pressure Switch
  • Expansion Vessel Re-pressurisation

Related codes

Full explanation for E119
E125

Your boiler is overheating because the water is not moving around the system properly.

High DIY-safe £180-350

What to check first

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

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E125
E128

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

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for E128
E129

Your boiler is struggling to keep a steady flame alight and has failed to correctly calibrate its burner settings after several attempts.

High Engineer only £120-280

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for E129
E130

Your boiler has detected 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
  • Main PCB
  • Heat Exchanger cleaning

Related codes

Full explanation for E130
E131

Your boiler has shut down because the exhaust gases have reached a temperature that is too high, posing a safety risk.

High Engineer only £120-350

Parts commonly replaced

  • Flue Thermistor
  • Heat Exchanger
  • Fan Assembly

Related codes

Full explanation for E131
E133

Your boiler is struggling to light or stay lit because gas isn't reaching the burner or the flame isn't being detected.

High DIY-safe £100-£350

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your gas meter.
  2. Try resetting the boiler by pressing the reset button for five seconds.
  3. If it is freezing outside, check that the white plastic condensate pipe leading outdoors isn't frozen solid.

Parts commonly replaced

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

Related codes

Full explanation for E133
E134

Your boiler is struggling to ignite because it has tried to start several times but cannot detect a flame or gas flow.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for E134
E135

Your boiler has lost its connection to the gas supply or is suffering from an internal component failure that prevents it from staying lit.

High Engineer only £150-350

Parts commonly replaced

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

Related codes

Full explanation for E135
E154

Your boiler has detected that the water temperature readings are inconsistent, which usually means the water isn't flowing correctly or a sensor has failed.

High Engineer only £120-250

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, causing the system to shut down for safety.

High Engineer only £200-£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 away waste gases is not spinning at the correct speed or has failed to start.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for E160 / E161
E163

Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning it cannot heat the water correctly or safely.

High Engineer only £90-160

Parts commonly replaced

  • DHW NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for E163
E164

Your boiler has detected an issue with the sensor that monitors water pressure, meaning it cannot confirm there is enough water to run safely.

High Engineer only £130-220

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 is struggling to communicate with the rest of the system.

High Engineer only £240-£380

Parts commonly replaced

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

Related codes

Full explanation for E167
E168

Your boiler's internal computer has encountered a memory error and has stopped working to protect your system.

High Engineer only £280-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E168
E193

Your boiler is struggling to move water around the system properly before it starts the heating process.

High DIY-safe £180-450

What to check first

  1. Check that your home's central heating valves and radiator valves are fully open
  2. Check the boiler pressure gauge and top it up to 1.5 bar if it is too low
  3. Gently bleed your radiators to remove any trapped air pockets
  4. Reset the boiler by pressing the reset button for five seconds

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor
  • Main PCB

Related codes

Full explanation for E193
E270

Your boiler is overheating because water isn't moving through the system properly, causing it to shut down for safety.

High DIY-safe £150-£350

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves and isolation valves are fully open
  3. Bleed your radiators to remove any trapped air pockets
  4. Reset the boiler using the reset button

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Flow/Return Thermistors

Related codes

Full explanation for E270
E317

Your boiler is having trouble with the electrical supply because the power coming into the unit does not match the required frequency.

High Engineer only £180-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Power Inverter (if applicable)

Related codes

Full explanation for E317
E321

Your boiler's hot water sensor has failed or is sending an incorrect signal, meaning the system cannot safely monitor the temperature of your water.

High Engineer only £90-160

Parts commonly replaced

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

Related codes

Full explanation for E321
Showing 111–120 of 129
E384

Your boiler thinks a flame is burning even when it shouldn't be, causing the system to lock itself down for safety.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for E384
E385

Your boiler is not receiving enough electrical power to operate safely, causing it to shut down.

High Engineer only £180-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Electrical wiring harness

Related codes

Full explanation for E385
E430

Your boiler is checking if there is enough water pressure to operate safely and has hit a temporary pause during this test.

Medium DIY-safe £60-120

What to check first

  1. Check the pressure gauge on your heating system (it should be between 1.0 and 1.5 bar).
  2. If the pressure is too low, use the filling loop to top up the water level.
  3. Restart the boiler using the reset button or by turning the power off and on.

Parts commonly replaced

  • Water pressure sensor
  • Filling loop valve

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

Your boiler is struggling to move water around the system effectively or is getting too hot too quickly.

High DIY-safe £120-£350

What to check first

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

Parts commonly replaced

  • Circulation Pump
  • Thermistor (NTC Sensor)
  • Heat Exchanger (Cleaning/Descaling)
Full explanation for H.01 – .05
H.01 – .08

Your boiler is overheating because water isn't moving through the system quickly enough to be cooled down.

High DIY-safe £120-£350

What to check first

  1. Check that your central heating valves and radiator valves are fully open
  2. Ensure your system pressure is topped up to between 1 and 1.5 bar
  3. Gently bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor (NTC)
  • Main PCB
Full explanation for H.01 – .08
H.01 – .14

Your boiler has detected that the water is getting too hot too quickly, likely because it cannot flow through the system properly.

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 your system pressure is between 1 and 1.5 bar on the pressure gauge.
  3. Reset the boiler using the reset button once the unit has cooled down.

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor (NTC Thermistor)
  • Main Heat Exchanger (if blocked with sludge)
Full explanation for H.01 – .14
H.01 – .18

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

High DIY-safe £180-450

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your system water pressure is between 1.0 and 1.5 bar
  3. Bleed your radiators to remove any trapped air pockets
  4. Press the reset button to see if the error clears

Parts commonly replaced

  • Circulation pump
  • Temperature sensors (NTC thermistors)
  • Main PCB
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 Engineer only £90-250

Parts commonly replaced

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

Your boiler has lost its configuration settings or has a memory error, meaning it currently doesn't know how to operate correctly.

High Engineer only £250-£450

Parts commonly replaced

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

Your boiler's internal computer is having a temporary communication hiccup regarding its specific setup settings.

High DIY-safe £100-280

What to check first

  1. Press the 'Reset' button on the front control panel for at least 5 seconds.
  2. Wait for the boiler to complete its restart sequence.
  3. If the fault persists, turn the main power switch to the boiler off and back on again.

Parts commonly replaced

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

Your boiler's internal computer is having a temporary glitch reading its settings, which is preventing it from starting up correctly.

High DIY-safe £180-350

What to check first

  1. Locate the reset button on the boiler control panel.
  2. Press and hold the reset button for at least 5 seconds.
  3. Wait for the boiler to complete its restart sequence and check if the error clears.

Parts commonly replaced

  • PCB (Main Control Board)
  • External Parameter Plug
Full explanation for H.02 – .04
H.02 – .06

Your boiler has detected that the water pressure is either too low or is leaking from the system, causing it to stop working for safety.

High DIY-safe £100-£350

What to check first

  1. Check the pressure gauge on your system; it should be between 1 and 1.5 bar.
  2. If the pressure is low, use the external filling loop valves to top up the system water.
  3. Inspect visible radiator valves and pipes for any signs of water leaks.

Parts commonly replaced

  • Auto Air Vent
  • Expansion Vessel
  • Pressure Relief Valve
  • Internal Seals
Full explanation for H.02 – .06
H.03 -.00

Your boiler is struggling to communicate with its internal temperature sensors, meaning it cannot accurately monitor heat levels and has stopped working as a safety precaution.

High Engineer only £120-£250

Parts commonly replaced

  • Flow/Return NTC Sensor
  • Flue Sensor
  • Wiring Loom
  • PCB
Full explanation for H.03 -.00
H.03 – .01

Your boiler's internal computer is having trouble talking to its main control board, 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
Full explanation for H.03 – .01
H.03 – .02

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

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances (like a hob) are working to ensure gas is reaching the property
  2. Check if your gas meter has credit (if using a prepayment meter)
  3. Press the Reset button once to see if the boiler restarts

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead
  • Printed Circuit Board (PCB)
Full explanation for H.03 – .02
OFF OFF OFF

Your boiler has no power, meaning the display is blank and the heating is not working at all.

High DIY-safe £0-120

What to check first

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

Parts commonly replaced

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

Your boiler has tried to light several times but failed, meaning it has now locked itself out for safety.

High DIY-safe £100-350

What to check first

  1. Check if your gas supply is active (for example, by testing a gas hob)
  2. Locate the reset button on the front control panel
  3. Press and hold the reset button for at least 5 seconds and release

Parts commonly replaced

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

Your boiler has detected an internal electrical communication problem and has shut down as a safety precaution.

High Engineer only £180-£450

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Low voltage wiring harness
  • Control knob assembly
Full explanation for ON ON ON