Biasi Antares System Fault codes & diagnostics

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

System Natural GasLPG 24-28 kW 2020-present

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Severity at a glance

Each cell = one fault code. Hover to identify.
6 Emergency 81 High 6 Medium 3 Low
Just want the most common Biasi Antares System faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 96 documented codes

Tap any card for details

1 +

Your boiler has failed to light because it cannot detect a flame, meaning you have no heating or hot water until it is reset or repaired.

High DIY-safe £90-280

What to check first

  1. Verify that your gas supply is turned on (check other gas appliances like a hob).
  2. Press the 'Reset' button on the front of the boiler once.
  3. Ensure there has not been a credit outage on your gas meter if you have a pre-payment system.

Parts commonly replaced

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

Related codes

Full explanation for 1 +
2 +

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

High DIY-safe £100-250

What to check first

  1. Wait 30 minutes for the boiler to cool down completely
  2. Check that all radiator valves are open and not blocked
  3. Press and hold the Reset button for 5-10 seconds to see if the system restarts

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger cleaning
Full explanation for 2 +
3 +

Your boiler has shut down completely because it detected a general operating fault and requires a manual reset to attempt to restart.

High DIY-safe £100-£350

What to check first

  1. Locate the selector switch on the front control panel.
  2. Turn the dial to the 'R' (Reset) position for five seconds.
  3. Return the dial to the 'On' or 'Winter' position and see if the boiler fires up.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for 3 +
4 +

Your boiler has detected that the water pressure is either too low or too high, or the water is not moving through the system correctly.

High DIY-safe £100-280

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
  2. If the pressure is below 1 bar, use the filling loop to top it up until it reaches the green zone.
  3. If the pressure is above 3 bar, bleed your radiators until the pressure drops back to 1.5 bar.

Parts commonly replaced

  • Water pressure sensor
  • Circulation pump
  • Expansion vessel
Full explanation for 4 +
5 +

Your boiler has stopped working because the internal fan, which safely exhausts fumes, is not turning at the correct speed or has failed to start.

High Engineer only £180-£350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air pressure switch
Full explanation for 5 +
6 +

Your boiler has detected that a temperature sensor responsible for tracking the water leaving the unit has stopped working correctly, and it has likely shut down to prevent overheating.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating (Flow) NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for 6 +
7 +

Your boiler is struggling to accurately measure the temperature of your hot water tank, which may prevent your water from heating up correctly.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW NTC thermistor sensor
  • Wiring harness
Full explanation for 7 +
8 +

Your boiler has lost connection with its outdoor temperature sensor, meaning it cannot automatically adjust itself based on the weather outside.

Low Engineer only £90-160

Parts commonly replaced

  • External NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 8 +
10

Your boiler has shut down completely because it detected dangerously high temperatures in the exhaust system.

Emergency Engineer only £150-£350

Parts commonly replaced

  • Flue gas probe
  • Thermal fuse
  • Heat exchanger cleaning kit
Full explanation for 10
10 +

Your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety feature to prevent damage or dangerous fumes.

Emergency Engineer only £150-£350

Parts commonly replaced

  • Flue gas probe
  • Thermal fuse
  • Heat exchanger cleaning kit
  • Main heat exchanger

Related codes

Full explanation for 10 +
Showing 11–20 of 96
11 +

Your boiler detects a flame when it shouldn't be there, causing the system to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation Probe
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for 11 +
12

Your boiler has stopped working because a sensor that monitors the temperature of the water returning to the unit has developed a fault.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor (sensor)
  • Sensor wiring harness

Related codes

Full explanation for 12
12 +

Your boiler has detected a fault with a temperature sensor that monitors the water returning to the unit, causing the heating to stop working.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness connector

Related codes

Full explanation for 12 +
13

Your boiler has detected that the water is getting too hot too quickly, usually because the water isn't flowing through the system as it should.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure the boiler pressure is between 1 and 1.5 bar
  3. Check for any visible leaks around the pipework
  4. Try restarting the boiler using the reset button

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger (de-scaling)
  • Thermistor (NTC sensor)

Related codes

Full explanation for 13
13 +

Your boiler is overheating because the water is not flowing through the system quickly enough to shed heat.

High DIY-safe £120-350

What to check first

  1. Check that at least two or three radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1 and 1.5 bar
  3. Rotate the pump screw gently if it appears seized
  4. Reset the boiler once you have checked the water flow

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • NTC Temperature Sensors

Related codes

Full explanation for 13 +
14

Your boiler has shut down because it is getting too hot or the water is not circulating properly through the system.

High DIY-safe £180-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Check for any visible leaks around the central heating pump

Parts commonly replaced

  • Circulating Pump
  • Overheat Thermostat
  • Main Heat Exchanger (if blocked)

Related codes

Full explanation for 14
14 +

Your boiler has shut down because it is getting too hot or the water is not circulating through the system correctly.

High DIY-safe £180-450

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Bleed any air out of your radiators
  4. Gently restart the boiler using the reset button

Parts commonly replaced

  • Circulating Pump
  • Main Heat Exchanger
  • Overheat Thermostat

Related codes

Full explanation for 14 +
15

Your boiler has stopped working because water is not flowing through the system quickly enough to prevent it from getting too hot.

High DIY-safe £120-£350

What to check first

  1. Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge.
  2. Ensure all radiator valves are fully open.
  3. Check if any bypass valves or external pumps are switched off.

Parts commonly replaced

  • Circulation pump
  • Primary heat exchanger
  • Return filter

Related codes

Full explanation for 15
15 +

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

High DIY-safe £150-£350

What to check first

  1. Check that your radiator valves are open, especially the lockshield valves.
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar on the pressure gauge.
  3. Try bleeding your radiators to remove any trapped air that might be blocking circulation.

Parts commonly replaced

  • Circulation pump
  • Central heating filter (cleaning/replacement)
  • Main heat exchanger

Related codes

Full explanation for 15 +
16

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

High Engineer only £120-300

Parts commonly replaced

  • Flue NTC sensor
  • Main heat exchanger
  • Pump

Related codes

Full explanation for 16
Showing 21–30 of 96
16 +

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

High Engineer only £120-£350

Parts commonly replaced

  • Flue NTC Sensor
  • Main Heat Exchanger
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 16 +
18

Your boiler has stopped because it cannot detect a change in temperature when it starts up, suggesting the water isn't 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 1.0 and 1.5 bar on the gauge
  3. Gently bleed air from your radiators using a radiator key

Parts commonly replaced

  • Circulation pump
  • Flow/Return thermistors
  • Main Heat Exchanger

Related codes

Full explanation for 18
18 +

Your boiler has stopped because it cannot detect a temperature difference when trying to heat up, which usually means water isn't 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 system pressure is between 1.0 and 1.5 bar on the gauge
  3. Bleed all radiators to remove trapped air
  4. Reset the boiler using the control knob

Parts commonly replaced

  • Circulation Pump
  • Temperature NTC Sensors
  • Main Heat Exchanger

Related codes

Full explanation for 18 +
19

Your boiler has detected a problem with one of its internal monitoring sensors, which means it cannot accurately measure temperature or pressure to operate normally.

High Engineer only £100-£220

Parts commonly replaced

  • External NTC thermistor
  • Auxiliary temperature probe
  • Wiring harness

Related codes

Full explanation for 19
19 +

Your boiler's internal computer has lost contact with a secondary temperature sensor, which means the system cannot accurately monitor the water temperature.

Medium Engineer only £90-180

Parts commonly replaced

  • NTC Temperature Probe
  • Sensor Wiring Harness
  • Main PCB

Related codes

Full explanation for 19 +
20

Your boiler has detected an internal electrical fault with its gas valve control system and has shut down for safety.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 20
20 +

Your boiler has detected an internal electrical failure with the control board that operates the gas valve, causing the system to shut down for safety.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for 20 +
21

Your boiler has detected an internal electrical fault with the gas valve control system and has shut down for safety.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Gas Valve

Related codes

Full explanation for 21
21 +

Your boiler has detected an internal electrical failure involving the gas valve control, meaning it cannot safely ignite and has shut down for safety.

High Engineer only £180-£350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Gas Valve

Related codes

Full explanation for 21 +
22 +

Your boiler has detected a flame when it should have gone out, suggesting a safety issue where gas might still be burning even after the control valve has closed.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Flame Sensing Electrode
  • Control PCB
Full explanation for 22 +
Showing 31–40 of 96
23

Your boiler is unable to control the flow of gas correctly to heat your home, which has caused the system to stop working for safety.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Wiring harness
  • Main circuit board (PCB)
Full explanation for 23
23 +

Your boiler is unable to control the flow of gas correctly because a vital connection to the gas control valve has been lost.

High Engineer only £140-260

Parts commonly replaced

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

Related codes

Full explanation for 23 +
24

Your boiler has detected that waste gases cannot properly escape through the outdoor flue pipe, causing it to shut down for safety.

Emergency Engineer only £100-280

Parts commonly replaced

  • Flue fan
  • Air pressure switch
  • Plume kit seals

Related codes

Full explanation for 24
24 +

Your boiler has detected that waste gases cannot properly escape through the flue pipe, often caused by an external blockage or a sensor fault.

Emergency Engineer only £100-£250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi tube

Related codes

Full explanation for 24 +
25

Your boiler is failing to keep its burner lit after multiple attempts, which has caused the system to shut down for safety.

High DIY-safe £100-300

What to check first

  1. Check that your gas prepay meter has credit
  2. Ensure other gas appliances in your home (like a hob) are working
  3. Press the Reset button once to see if the system restarts

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve
  • Spark generator

Related codes

Full explanation for 25
25 +

Your boiler is failing to keep the flame lit after several attempts, causing the system to shut down for safety.

High DIY-safe £100-350

What to check first

  1. Check that your gas meter has credit (if on a prepay meter)
  2. Check that other gas appliances, like a hob, are working correctly
  3. Reset the boiler by turning the control knob to 'R' for five seconds

Parts commonly replaced

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

Related codes

Full explanation for 25 +
26

Your boiler has detected that its internal temperature sensors disagree with each other, causing it to shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Heating NTC Thermistor
  • Flow/Return Sensor
  • Main PCB

Related codes

Full explanation for 26
26 +

Your boiler has shut down because its internal temperature sensors are giving very different readings, suggesting a circulation problem or a failing component.

High Engineer only £120-250

Parts commonly replaced

  • NTC Temperature Sensor
  • Circulating Pump
  • Main PCB

Related codes

Full explanation for 26 +
40

Your boiler has detected an issue with the electrical power supply frequency coming into the unit, which is preventing it from running safely.

High Engineer only £100-350

Parts commonly replaced

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

Related codes

Full explanation for 40
40 +

Your boiler has detected an issue with the electrical power timing coming into the unit, which is preventing it from running safely.

High Engineer only £100-£350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • External Voltage Regulator
Full explanation for 40 +
Showing 41–50 of 96
42

Your boiler's control buttons or internal panel have stopped communicating correctly with the main computer.

High Engineer only £180-350

Parts commonly replaced

  • Control Interface / Keypad
  • PCB (Main Circuit Board)
  • Wiring Loom

Related codes

Full explanation for 42
42 +

Buttons or touch inputs on your boiler's control panel have become stuck, unresponsive, or have been pressed for too long.

Medium DIY-safe £100-280

What to check first

  1. Turn the boiler power off at the fused spur switch for 30 seconds.
  2. Gently wipe the control panel with a dry microfiber cloth to ensure no buttons are physically stuck or obstructed by dirt.
  3. Turn the power back on and see if the code clears.

Parts commonly replaced

  • User interface panel
  • Main PCB

Related codes

Full explanation for 42 +
44 +

Your boiler is failing to light the gas properly and has locked itself out for safety after several unsuccessful attempts.

High Engineer only £150-350

Parts commonly replaced

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

Related codes

Full explanation for 44 +
50

Your boiler is having trouble talking to your external heating controls or smart thermostat, meaning it cannot receive the correct instructions to heat your home.

High DIY-safe £90-180

What to check first

  1. Check that your wall thermostat or smart hub is powered on and has fresh batteries if required.
  2. Ensure any wireless receiver boxes plugged into the wall are switched on and showing a green light.
  3. Try resetting the boiler by turning the dial to 'Reset' for five seconds and then back to the on position.

Parts commonly replaced

  • OpenTherm Bridge
  • External Thermostat
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 50
50 +

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

Medium DIY-safe £90-250

What to check first

  1. Check that your room thermostat or smart hub is powered on.
  2. Replace the batteries in your wall-mounted thermostat.
  3. Restart the boiler by switching it off and back on at the fused spur.

Parts commonly replaced

  • OpenTherm Bridge/Receiver
  • Room Thermostat
  • PCB
Full explanation for 50 +
62

Your boiler is requesting a calibration routine to ensure the gas and air are burning correctly, which often happens after a power interruption or part replacement.

Medium DIY-safe £0-120

What to check first

  1. Locate the reset button or selector switch on the front control panel.
  2. Turn the selector to the 'Reset' position for 5 seconds and then back to 'On'.
  3. Observe the boiler for several minutes while it performs its automated calibration cycle.

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 62
62 +

Your boiler needs to run a self-tuning process to ensure it is burning gas efficiently and safely.

Low DIY-safe £0-120

What to check first

  1. Locate the 'Reset' button on the front control panel.
  2. Press and hold the Reset button for 2 to 5 seconds.
  3. Wait while the boiler performs its automatic calibration sequence; it may make several noises until it returns to normal operation.

Parts commonly replaced

  • No parts required (Software reset)
  • Ionisation Electrode (if calibration fails)
  • Gas Valve (if calibration fails)
Full explanation for 62 +
65

Your boiler is struggling to burn gas correctly and has shut down as a safety precaution to prevent unstable combustion.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for 65
65 +

Your boiler is struggling to manage its flame correctly and has shut down as a safety precaution.

High Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Main PCB
  • Ignition electrode
Full explanation for 65 +
68

Your boiler is struggling to get enough gas to stay lit or run safely.

High DIY-safe £100-350

What to check first

  1. Check if your gas meter has credit (if you are on a prepay meter)
  2. Check that your main gas stopcock is fully open
  3. Check if other gas appliances, like a cooker, are working correctly to rule out a wider gas supply issue

Parts commonly replaced

  • Gas Valve
  • Gas Meter Regulator
  • Printed Circuit Board (PCB)
Full explanation for 68
Showing 51–60 of 96
68 +

Your boiler is not receiving enough gas to stay lit safely, which is preventing your heating and hot water from working.

High Engineer only £100-280

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Inlet Gas Pipework
Full explanation for 68 +
77 +

Your boiler's electronic control system is sending the wrong signals to the internal gas valve, causing the unit to shut down for safety.

High Engineer only £140-£350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Gas Valve Modulator Coil

Related codes

Full explanation for 77 +
78

Your boiler is struggling to receive a steady supply of gas, which is preventing it from firing up correctly.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, such as a gas hob, are working correctly to rule out a general gas supply issue.
  2. Ensure your gas meter has credit if you use a prepay meter.
  3. Verify that the gas isolation valve under the boiler is fully open.

Parts commonly replaced

  • Gas Valve
  • Gas Meter Regulator
  • Spark Electrode
Full explanation for 78
78 +

Your boiler is struggling to get enough gas to stay lit, which has caused it to stop heating your home.

High Engineer only £100-£350

Parts commonly replaced

  • Gas valve
  • Flame sensing electrode
  • Inlet gas filter
Full explanation for 78 +
79

Your boiler's internal computer has lost communication with the gas control valve, meaning it cannot safely regulate the flame.

High Engineer only £140-£320

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Modulator Coil
  • Wiring Harness

Related codes

Full explanation for 79
79 +

Your boiler is having trouble controlling the flame intensity because of a software or internal communication error.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Modulator Coil
  • Gas Valve

Related codes

Full explanation for 79 +
89

Your boiler has detected an issue with its internal computer board or the electricity supply coming into your home, which has caused it to stop working.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Surge Protector
Full explanation for 89
89 +

Your boiler has detected an internal computer error or an unstable electrical supply that is preventing it from running safely.

High DIY-safe £250-£450

What to check first

  1. Turn the boiler off at the main electrical switch and wait for 30 seconds
  2. Turn the power back on and press the 'Reset' button
  3. Check if other electrical appliances in the home are behaving strangely, which may indicate a grid issue

Parts commonly replaced

  • Main Control PCB
  • Electrical Surge Protector
Full explanation for 89 +
91

Your boiler has been manually reset too many times after failing to ignite, causing it to lock you out for safety until it is checked by a professional.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensing probe
Full explanation for 91
91 +

Your boiler has been manually reset too many times in a short period and has now locked itself as a safety precaution.

High Engineer only £100-250

Parts commonly replaced

  • Main PCB
  • Ignition Electrode
  • Gas Valve
Full explanation for 91 +
Showing 61–70 of 96
96

Your boiler has detected an issue with the electrical power supply frequency, which means it cannot safely coordinate its internal timing and operations.

High Engineer only £120-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Voltage Regulator

Related codes

Full explanation for 96
96 +

Your boiler has shut down completely because it has experienced multiple repeated technical errors and is now locked for safety.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for 96 +
97

Your boiler is not receiving enough electrical power to operate correctly, which usually means there is an issue with your home's electricity supply or the boiler's internal circuit board.

High Engineer only £120-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Voltage Regulator
  • Electrical Wiring Harness

Related codes

Full explanation for 97
E01

Your boiler has failed to light or cannot detect a flame, meaning your heating and hot water will not work until it is reset or repaired.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to ensure gas supply.
  2. Ensure your prepaid gas meter has credit if applicable.
  3. Press and hold the Reset button for 2 to 3 seconds to see if the boiler restarts.

Parts commonly replaced

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

Related codes

Full explanation for E01
E02

Your boiler has switched itself off to prevent overheating, usually because the water inside has become too hot.

High DIY-safe £100-280

What to check first

  1. Check that your radiator valves are open to allow water to flow.
  2. Check your boiler pressure gauge and top it up to 1.5 bar if it is too low.
  3. Press the 'Reset' button on the boiler control panel to see if the fault clears.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger

Related codes

Full explanation for E02
E03

Your boiler has shut down because it detected that the exhaust gases are too hot or a safety fuse has blown to prevent overheating.

High Engineer only £120-250

Parts commonly replaced

  • Flue NTC sensor
  • Thermal fuse
  • Heat exchanger cleaning

Related codes

Full explanation for E03
E04

Your boiler has detected that there is either not enough water pressure in the system or the water is not moving through the pipes as it should.

High DIY-safe £100-£350

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
  2. If the pressure is too low, use the filling loop valves under the boiler to top up the water pressure.
  3. Reset the boiler once the correct pressure has been reached.

Parts commonly replaced

  • Circulation pump
  • Water pressure switch
  • Expansion vessel

Related codes

Full explanation for E04
E05

Your boiler has stopped working because the fan that helps remove waste gases is not spinning at the correct speed.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for E05
E06

Your boiler has stopped working because it can no longer accurately measure the temperature of the water inside the system.

High Engineer only £90-160

Parts commonly replaced

  • Main circuit NTC temperature sensor
  • Connecting wiring harness

Related codes

Full explanation for E06
E07

Your boiler has detected a fault with the sensor that measures the temperature of the water returning from your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC temperature sensor
  • Connecting wiring harness

Related codes

Full explanation for E07
Showing 71–80 of 96
E08

Your boiler has lost connection with its outdoor thermometer, meaning it cannot automatically adjust its temperature based on the weather outside.

Low Engineer only £90-160

Parts commonly replaced

  • External temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for E08
E10

Your boiler's internal sensor is unable to detect the water pressure, causing the system to stop working for safety.

High Engineer only £140-£220

Parts commonly replaced

  • Water pressure transducer
  • Wiring harness connector
  • Main PCB

Related codes

Full explanation for E10
E11

Your boiler thinks a flame is present even though the burner should be switched off, which is a safety conflict causing the system to lock out.

Emergency Engineer only £120-300

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Main PCB

Related codes

Full explanation for E11
E14

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

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 and 1.5 bar
  3. Check for any signs of an external system blockage or frozen pipes

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensors
  • Main Heat Exchanger

Related codes

Full explanation for E14
E15

Your boiler has sensed that the water returning from your radiators is hotter than the water leaving the boiler, which usually indicates an internal sensor error or a problem with water circulation.

High Engineer only £90-180

Parts commonly replaced

  • Return NTC thermistor
  • Flow NTC thermistor
  • Main PCB

Related codes

Full explanation for E15
E16

Your boiler has switched itself off because the sensor that monitors the temperature of the exhaust gases is no longer working correctly.

High Engineer only £90-180

Parts commonly replaced

  • Flue NTC temperature probe
  • Wiring harness connectors

Related codes

Full explanation for E16
E20

Your boiler is failing to light the gas or cannot recognise that a flame has started, preventing it from heating your home.

High DIY-safe £120-350

What to check first

  1. Check that your gas emergency control valve is open and other gas appliances are working
  2. Press the 'Reset' button on the boiler control panel for 2-3 seconds
  3. Check that your external condensate pipe hasn't frozen if the weather is extremely cold

Parts commonly replaced

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

Related codes

Full explanation for E20
E21

Your boiler's main control centre has suffered an internal electrical failure and can no longer manage the system's functions.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for E21
E22

Your boiler's internal computer has lost its settings or is having trouble communicating with the system's software.

High Engineer only £180-320

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • PCB Programming Key

Related codes

Full explanation for E22
E24

Your boiler has been forced to shut down because it detected a dangerous build-up of heat before it even finished starting up.

High Engineer only £120-250

Parts commonly replaced

  • Safety thermostat (Limit stat)
  • Circulation pump
  • Primary heat exchanger

Related codes

Full explanation for E24
Showing 81–90 of 96
E65

Your boiler is struggling to manage its flame correctly and has shut down as a safety precaution.

High Engineer only £150-380

Parts commonly replaced

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

Related codes

Full explanation for E65
E68

Your boiler is struggling to operate because it is not receiving a steady or sufficient supply of gas to stay lit.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, such as a hob, are working correctly to rule out a general gas supply issue
  2. If you have a prepayment meter, ensure you have sufficient credit available
  3. Check that your external gas emergency control valve is fully open

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Gas Pressure Regulator

Related codes

Full explanation for E68
E69

Your boiler has lost its internal connection between the control panel and the main system, meaning it cannot receive or send the signals needed to operate.

High Engineer only £120-£350

Parts commonly replaced

  • Main PCB
  • Wiring Loom
  • User Interface Panel

Related codes

Full explanation for E69
E77

Your boiler's control system is struggling to adjust the flame size correctly, which may lead to inefficient heating or the unit shutting down.

Medium Engineer only £120-£350

Parts commonly replaced

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

Related codes

Full explanation for E77
E78

Your boiler is struggling to operate because it is not receiving a steady or sufficient supply of gas.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances in your home, such as a gas hob or fire, are working correctly.
  2. If you have a prepayment gas meter, verify that you have sufficient credit.
  3. Check that your external gas emergency control valve is fully open.

Parts commonly replaced

  • Gas Valve
  • Gas Meter Regulator
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E78
E79

Your boiler is having trouble controlling the flame size correctly, which is preventing the system from heating your home efficiently or safely.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Modulating Coil

Related codes

Full explanation for E79
E89

Your boiler's electronic brain is struggling to process the incoming electrical power properly or has developed an internal hardware fault.

High Engineer only £280-550

Parts commonly replaced

  • Main Circuit Board (PCB)
  • Mains Filter

Related codes

Full explanation for E89
E91

Your boiler has been manually reset too many times within a short period and has now disabled itself for safety reasons.

High DIY-safe £0-120

What to check first

  1. Turn off the power supply to the boiler at the fused spur switch
  2. Wait for approximately 30 to 60 seconds
  3. Turn the power back on to allow the system to clear the temporary lockout memory

Parts commonly replaced

  • None (Software reset required)
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for E91
E96

Your boiler has detected an issue with the electrical power supply frequency, which prevents it from operating safely.

High Engineer only £100-£350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • External voltage regulator

Related codes

Full explanation for E96
E96+

Your boiler has shut down completely because it has experienced several recurring faults in a short period and requires a professional reset and inspection.

High Engineer only £100-350

Parts commonly replaced

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

Related codes

Full explanation for E96+
Showing 91–96 of 96
E97

Your boiler has detected that the electricity supply arriving at the unit is too low for it to operate safely and has shut down to protect its internal parts.

High Engineer only £100-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Stabilizer

Related codes

Full explanation for E97
E99

Your boiler has experienced a major internal communication failure or a software logic error that has caused it to shut down for safety.

High DIY-safe £180-450

What to check first

  1. Locate the reset button or dial on the front control panel.
  2. Press or turn to the 'Reset' position for 5 seconds and release.
  3. Wait 2 minutes to see if the boiler restarts; if the code returns immediately, a professional is required.

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E99
Keys fault

Your boiler's internal computer has detected a problem with its settings or the identification key that tells it how to operate.

High Engineer only £120-350

Parts commonly replaced

  • Main PCB
  • Software Key
  • Internal Wiring Harness
Full explanation for Keys fault
L1

Your boiler is overheating while trying to heat your tap water, causing it to shut down for safety.

High DIY-safe £120-350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the pressure gauge.
  2. Ensure all radiator valves are fully open to help heat dissipate.
  3. Try resetting the boiler by turning the control knob to 'R' for five seconds.

Parts commonly replaced

  • DHW Temperature Sensor (NTC)
  • Main Heat Exchanger (Descaling)
  • Diverter Valve

Related codes

Full explanation for L1
Lock state

Your boiler has switched itself off because the water inside the system has become too hot.

High DIY-safe £100-280

What to check first

  1. Check that your radiator valves are fully open to allow water to circulate.
  2. Ensure there is enough water pressure in the system by checking the pressure gauge is between 1 and 1.5 bar.
  3. Wait for the boiler to cool down and try pressing the reset button.

Parts commonly replaced

  • Limit Thermostat
  • Circulation Pump
  • Heat Exchanger
Full explanation for Lock state
max err .

Your boiler has failed to complete its automatic self-adjustment process, which is necessary for it to run efficiently and safely.

High DIY-safe £100-350

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
  3. Wait up to 10 minutes for the boiler to attempt the calibration cycle again

Parts commonly replaced

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

Related codes

Full explanation for max err .