Common UK Boiler Fault Codes & What They Mean
Boilers play a vital role in keeping our homes warm and providing hot water. However, they can occasionally encounter faults that are indicated by specific error codes. Understanding these fault codes can help you identify potential issues with your boiler and take appropriate action. In this article, we will provide you with a guide to common boiler fault codes in the UK, along with their meanings, for several popular boiler manufacturers.
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Baxi Boiler Fault Codes
Duotec/ Platinum range
E10: Flame loss during operation.
E119: Low water pressure switch activated. Low pressure in the system or pressure sensor faulty.
E133: Ignition lockout.
E168: PCB (printed circuit board) fault.
E160: Fan fault.
E130: Flue NTC operated
E193; Pre-Circulation fault
E125: Circulation fault
E110: Safety thermostat operated
E50: Hot water NTC fault
E28: Flue NTC fault, air pressure switch, blocked flue, blocked condensate or wiring fault
Baxi 600/800 Range
E09: Gas valve connection cable.
E10: External probe fault.
E12: Differential water flow switch fault (still open).
E13: Differential water flow switch fault (still closed).
E15: Gas valve command fault.
E20: Central heating NTC fault.
E28: Flue NTC fault.
E40: Central heating return NTC fault.
E50: DHW NTC sensor fault (tank boiler) (s.c.) OR DHW NTC sensor fault (tank boiler) (o.c.).
E83/E84/E85/E86/E87: No communication.
E109: Pre-circulation fault.
E110: i) Boiler max temperature exceeded for gradient (probable pump jammed or air in the circuit). OR ii) Boiler max temperature exceeded for overtemperature (probable pump jammed or air in the circuit). OR iii) Safety thermostat sensor tripped.
E118: Primary system water pressure too low (< 0.5 bar).
E125: Circulation fault (primary).
E128: Frequent flame failure (12 times).
E129: Safety error for frequently loss of flame with max correction during the ignition during Calibration Function.
E130: Flue thermostat sensor tripped (lockout).
E133: Failure to light (could be a gas supply issue).
Check that the gas supply is available. If possible try lighting a gas cooker or fire.
E134: Elapsed time gas valve open without gas (short request in a short period)
E135: Interruption of gas supply (internal error).
E154: Flow/return sensor temperature test.
E160: Fan or fan wiring fault.
E163: Domestic Hot Water NTC sensor fault (s.c.) OR Domestic Hot Water NTC sensor fault (o.c.).
E270: Circulation fault (dry fire).
E317: Wrong power supply electrical frequency (Hz).
E321: Hot water NTC fault.
E384: False flame.
E385: Under voltage.
E430: Water pressure temporary test.
E430 + Flame ‘crossed’ Water pressure test failed.
Glow-Warm Boiler Fault Codes
Ultracom₂ cxi range
F00 Flow heating temperature sensor fault
F01 Return heating temperature sensor fault
F10 Flow heating temperature sensor fault
F11 Return heating temperature sensor fault
F20 Overheating fault
F22 Low water pressure
F23 Water circulation fault
F24 Water circulation fault
F26 Fault in gas valve
F27 Flame detection fault
F28 Ignition fault
F29 Loss of flame during operation
F32 Incorrect air pressure
F49 EBUS voltage fault
F61 Fault in the main board
F62 Fault in the main board
F63 Fault in the main board
F64 Fault in the main board
F65 Fault in the main board
F67 Fault in the main board
F68 Fluctuation of flame signal
F70 User interface incompatible with the main board
F71 Flow heating temperature sensor fault
F72 Permanent temperature difference between flow and return heating sensors
F73 Heating circuit pressure sensor fault
F74 Heating circuit pressure sensor fault
F76 Thermal fuse fault
F77 Fault in gas valve motor
F83 No water in the installation
F84 Permanent temperature difference between flow and return heating sensors
F85 Flow and Return heating sensor fault
F86 Underfloor heating contact fault
Err User interface fault
Flexicom cx range
F1 Ignition fault
F3 Fan unable to reach ignition speed
F4 Ignition fault
F5 Overheat Fault
F6 Central heating flow thermistor
F7 Domestic hot water thermistor
F9 Water pressure sensor fault, blocked flow filter or pump fault
F10 Central return flow thermistor
F11 Flow and or return thermistor fault
F13 PCB memory or sensing fault
F14 Gas valve control defective
F15 E-bus voltage failure
F22 Low water pressure or ignition temperature rise too slow
F24 Central heating return temperature > 90 degrees
F25 Circulation fault
F43 Generic error
F70 Software incompatible
F73 Unable to see pump activate
F77 Condensate pump error (optional)
Flexicom cx range
F.00 Fault: Flow temperature sensor NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective
F.01 Fault: Return temperature sensor NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective
F.10 Short circuit: Flow temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing
F.11 Short circuit: Return temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing
F.12 and F.91 Short circuit: Cylinder temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing
F.13 Short circuit: Domestic hot water cylinder temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing
F.20 Safety switch-oft. Overheating temperature reached Incorrect earth connection between cable harness and product, flow or return NTC defective (loose connection), black discharge viaignition cable, ignition plug or ignition electrode
F.22 Safety switch-oft. Low water pressure in the boiler No or insufficient water in the product, water pressure sensor defective, cable lo the pump or to the water pressure sensor loose/not connected/defective
F.23 Safety switch-oft. Temperature difference too great (NTC1/NTC2) Pump blocked, insufficient pump output, air in product, flow and return NTC sensor connected the wrong way round
F.24 Safety switch-oft. Temperature rise too fast Pump blocked, insufficient pump output, air in product, system pressure too low, non-return valve blocked/incorrectly installed
F.25 Safety switch-off. Flue gas temperature too high Breaking plug connection for optional flue gas safety temperature limiter (STB), break in cable harness
F.27 Safety switch-off. Fault in flame detection Moisture on the electronics, electronics (flame monitor) defective. gas solenoid valve leaking
F.28 Fault: Ignition unsuccessful when starting up Gas meter defective or gas pressure monitor has triggered, air in gas, gas flow pressure too low, thermal isolator device (TAE) has triggered, incorrect gas restrictor, incorrect spare gas valve, fault on the gas valve, multiple plug on PCB incorrectly plugged in, break in cable harness, ignition system (ig
nition transformer, ignition cable, ignition plug, ignition electrode) defective, ionisation current interrupted (cable, electrode), incorrect earthing of product. electronics defective
F.29 Fault: Flame loss Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of product, ignition transformer has spark failure
F.32 Fan frost protection function active: Fan speed outside the tolerance values Plug on fan not correctly plugged in, multiple plug on PCB not correctly plugged in, break in cable harness, fan blocked, Hall sensor defective, electronics defective
F.33 Fan frost protection function active: Air pressure switch fault Pressure monitor has not switched or has switched at a fan speed value that is too high (insufficient air supply)
Pressure monitor plug not correctly plugged in, pressure monitor defective, hose removed from between the pressure monitor and silencer, air/flue pipe blocked
FA9 eBUS fault: Voltage too low Short circuit on eBUS. eBUS overload or two power supplies with different polarities on the eBUS
F.61 Fault: Gas valve control system Short circuit/short to earth in cable harness for the gas valve, gas valve defective (colls shorted to earth), electronics defective
F.82 Fault: Gas valve switch-off control Delayed switch-off of gas valve, delayed extinguishing of flame signal,gas valve leaking, electronics defective
F.83 Fault: EEPROM Electronics defective
F.64 Fault: Electronics/sensor/analogue-to-digital converter Flow or return NTC short circuited, electronics defective
F.85 Fault: Electronics temperature too high Electronics overheating due to external influences, electronics defective
F.67 Value sent back by ASIC is incorrect (flame signal) Implausible flame signal, electronics defective
F.88 Fault: Unstable flame (analogue input) Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas restrictor, ionisation flow interruption (cable, electrode)
F.70 Invalid product code (DSN) Display and PCB replaced at same time and Device Specific Number not reset, wrong or missing output range coding resistance
F.71 Fault: Flow/return temperature sensor Flow temperature sensor signalling constant value: Flow temperature sensor incorrectly positioned on supply pipe, flow temperature sensor defective
F.72 Fault: Deviation in the water pressure sensor/return temperature sensor Flow/return NTC temperature difference too great -> flow and/or return temperature sensor defective
F.73 Fault: Water pressure sensor not connected or has short-circuited Interruption/short circuit of water pressure sensor, short circuit to GND in supply line to water pressure sensor or water pressure sensor defective
F.74 Fault: Electrical problem in the water pressure sensor Line to water pressure sensor has a short circuit to 5 V/24 V or internal fault in the water pressure sensor
F.75 Fault: Pressure sensor Pressure switch defective
F.78 The safety cut-out in the primary heat exchanger is defective Safety cut-out feedback does not match the gas valve feedback
F.77 Fault: Condensate or smoke No response, flue non-return flap defective
F.78 Interruption to DHW outlet sensor at external controller UK ink box is connected, but hot water NTC not bridged
F.83 Fault: Burner temperature sensor Burner temperature sensor is defective
When the burner starts, the temperature change registered at the flow or return temperature sensor is non-existent or too small: insufficient water in the product, the flow or return temperature sensor is not in the correct position on the pipe
F.84 Fault: Flow/return temperature sensor Values not consistent, difference < -6 K
Flow and return temperature sensors signalling implausible values: Flow and return temperature sensors have been inverted, flow and return temperature sensors have not been correctly Installed
F.85 Fault: Temperature sensor The flow and/or return temperature sensors have been installed on the same pipe/incorrect pipe
Temperature sensor not connected or is connected incorrectly
F.88 Fault: Underfloor heating contact Underfloor heating contact open, sensor disconnected or defective
F.87 Fault: Electrodes Electrodes not connected or they are connected incorrectly, short circuit in the cable harness
F.88 Fault: Gas valve Gas valve not connected or it is connected incorrectly, short circuit in the cable harness
F.89 Fault: Pump, Pump not connected or it is connected incorrectly, incorrect pump connected, short circuit in the cable harness
Valliant Boiler Fault Codes
– F. 00 / F.0: Flow temperature sensor interruption
– F10: Flow NTC short circuit
– F11: Return NTC short circuit
– F22: Low water pressure Switch activated. Low pressure in system, if F75 also shows, the sensor is faulty
– F27: Flame loss during operation.
– F28/F29: Ignition fault. Possibly blocked/frozen condensate, regulator fault, gas supply fault & could also be a PCB fault
– F32: Fan error
– F75: Faulty pump or circulation issue/ water pressure sensor fault
– F83: Fault with the flue or air supply.
– F20: Boiler overheat or earth fault
– F54: Gas Valve fault
– F76: Thermal fuse blown. Main heat exchanger required
– F61/F62: PCB/Gas valve fault
Worcester Boiler Fault Codes
Greenstar-i fault codes
FD: Power interrupted
C7: Fan not running on start-up
C6: Fan speed too high or too low
C1: Fan stopping during operation
C4: Fan has failed to stop
E2: Flow temperature issue
E9: Primary flow temperature exceeding 95°
FA: Ionisation detected after gas valve closed
EA: No ionisation detected after ignition
F7: Ionisation detected before burner start
9U: Control box defective or loose
C4: Control box or heat control module defective
F0: Gas valve/control box error
A8: Heat control module invalid
CC: Outdoor sensor defect
A7: Domestic hot water sensor defect
A1: Pump stuck or running dry
E9: Flue or high limit thermostat activated
D4: Primary flow temps rising too fast
Greenstar-i fault codes
T1:Ignition test
T2: Fan test
T3: Pump test
T4: Three way valve test
T6: Ionisation oscillator test
9A 362: Incorrect HCM fitted
9U 233: Heat Control Module (HCM) error/Problem with code plug
B7 257: Internal error/Potential control board problem
C6 215: Fan problem/Fan running too fast
C7 214: Fan problem/Fan not running
D1 240: Return sensor error/Sensor may be wet or damaged
E2 222: Flow sensor short circuit error
E5 218: Flow temperature too high
E9 219: Safety sensor fault/Temperature too high, sensor short circuit or open circuit
EA 227: No flame detected or flame signal loss during operation
F0 237: Internal error
F7 228: Flame error/False flame or flame detected before burner started
FA 306: False flame fault/Flame detected after burner stop
FD 231: Mains power fault/Electrical power interruption
FA 364: Gas valve EV2 leak test failed /Gas valve leak
FB 365: Gas valve EV1 leak test failed
A1 281: Pump stuck or running with air in the system
C1 264: Airflow stopped during operation
C4 273: Airflow present during last 24 hour
D4 271: Temperature difference between flow and safety sensor exceeds limit
D1 240: Return sensor short circuit
E9 224: Max thermostat activated/ Flue gas thermostat overheat
EA 227: No ionisation detected after ignition
EF 349: Central heating boil detected / Boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return
NO CODE 212: Safety or flow temperature rising too fast
Worcester Bosch 8000 series
200 O: Boiler in heating mode
201 O: Fan not running on start-up
202 O: Boiler in anti-cycle mode
203 O: Boiler in stand-by mode
204 O: Current primary water temperature higher than set value
208 O: Chimney sweep demand
224 V: Safety temperature limiter has tripped – top-up water until the reset pressure is reached
227 V: No flame signal after ignition burner control unit could need replacing
228 V: Flame signal without flame present – air/gas ratio control valve may need replacing as might the ionisation cable
305 O: Boiler in hot water anti-cycle mode
306 V: Flame signal after closing the fuel supply – the air/gas ratio control valve might need replacing
360 V: Incompatible code plug – check if a correct code plug is installed and exchange or reconnect code plug
815 W/B: Low loss header temperature sensor faulty – check the sensor port or check the differential sensor for incorrect installation position or breakage
1010 O: No BUS communication cable, EMS-Bus isn’t connected or damaged – connect the cable for the EMS-Bus or replace the damaged cable exchange fuse
1017 W: Water pressure too low – the water needs topping up and the vent system or pressure sensor may need replacing
1021 B: Hot water temperature sensor is defective – the plug to the hot water temperature sensor may not be connected
1022 B: Hot water storage temperature sensor is defective – connect the plug to the hot water temperature sensor correctly, mount the hot water temperature sensor correctly or replace the hot water temperature sensor
1037 W: Outside temperature sensor is defective – check the connecting lead
1065 B: Pressure sensor defective or not connected – check pressure sensor connection as it may need replacing
1068 W: Outside temperature sensor defective – check the connecting lead
1073 W: Short circuit of the flow temperature sensor – the temperature sensor may need replacing
1074 W: No signal from the flow temperature sensor available – connect the plug to the flow temperature sensor correctly or temperature sensor could need replacing
1075 W: Short circuit of the temperature sensor at the heating block – temperature sensor may need replacing
1076 W: No signal from the temperature sensor at the heating block available – replace the temperature sensor, the connecting lead or the control unit
2920 V: Error with the flame monitoring
2924 V: No feedback from the modulating gas valve. The gas valve relay is defective – press the reset button and apply burner start, wait to see if fault reoccurs, if it does the gas valve needs replacing
2925 V: Feedback from the modulating gas valve is too low
2927 B: Flame failed during burner operation. Open the main shut off valve, shut down the appliance and check gas line, replace the ionisation electrode, set burner correctly and minimum rated load, check the integrity flue system and if the interconnected room air supply is too small, or the size of the ventilation opening is too small, clean the heating block on the flue gas side or replace the control unit/burner control unit
2946 V: Incorrect code plug detected – the code plug needs replacing
2948 B: No flame signal. With low output the burner starts automatically after cleaning. If the fault occurs repeatedly, the setting of the CO2 valves need checking
2963 B: Signal from flow and heat exchanger temperature sensor outside the permissible range – the connecting lead needs connecting correctly
2964 B: Flow rate in heat exchanger is too low
2965 B: Flow temperature too high
2966 B: Flow temperature rise in heat exchanger too rapid
2967 B: Flow / heat exchanger temperature sensor differential too great
2970 B: Pressure drop in heating system too rapid
2971 B: System pressure too low – the heating system needs venting or water needs topping up until the preset pressure is reached. Replace the cable to the pressure sensor replace the pressure sensor
Ideal Boiler Fault Codes
FD – Insufficient Water Flow
When your Ideal boiler displays the FD fault code, it means that there is inadequate water flow in your heating system. This indicates that the boiler is not detecting sufficient water. To resolve this issue, you can easily repressurize the boiler, restoring the water pressure to the optimal level.
F1 – Low Water Pressure
The F1 fault code on your Ideal boiler indicates that the water pressure is too low, causing the boiler to stop functioning properly and impairing its performance. You can rectify this issue by adjusting the pressure to the recommended level of 1.5 bars.
F2 – Flame Loss
If your Ideal boiler displays the F2 fault code, it means that the flame has been lost. This can occur due to the age or inefficiency of the boiler. To address this issue, it is essential to contact a Gas Safe-registered engineer who can diagnose and resolve the problem professionally.
F3 – Fan Fault
The F3 fault code indicates that there is a problem with the fan of your boiler. This issue could be caused by a loose or damaged fan. Resolving this complex problem requires the expertise of a qualified professional.
F4 – Thermistor Fault
The F4 fault code on your Ideal boiler points to an issue with the flow thermistor, typically related to circulation problems. Unfortunately, this fault cannot be resolved through DIY methods and requires the assistance of a professional heating engineer.
F5 – Return Thermistor Fault
The F5 fault code on your Ideal boiler indicates a problem with the return thermistor. This fault may be caused by operational issues or a damaged connection. It is recommended to contact a Gas Safe engineer to diagnose and fix this problem.
F6 – Outside Sensor Fault
The F6 fault code on your Ideal boiler suggests a problem with the outside temperature sensor. This could be due to a faulty or damaged sensor. To address this issue, it is advisable to consult a Gas Safe engineer as the problem may be related to the Printed Circuit Board (PCB).
F7 – Low Mains Voltage
The F7 fault code on your Ideal boiler indicates a problem with the main electricity supply to your property. If the voltage drops below 190 VAC, it is necessary to contact a Gas Safe engineer to investigate and resolve the issue.
F9 – Printed Circuit Board (PCB) Fault
The F9 fault code on your Ideal boiler indicates a problem with the Printed Circuit Board (PCB). Repairing a faulty PCB can be quite expensive, so it is worth considering options such as investing in a new boiler or exploring financing options for a replacement.
Lack of Water Flow (L1): The L1 fault code indicates inconsistent water flow, resulting in either low or high temperatures. To resolve this issue, try resetting your boiler. If the problem persists, contact a Gas Safe engineer for further assistance.
Ignition Lockout (L2): The L2 fault code indicates ignition lockout caused by blockages or a frozen condensate pipe. Contact a Gas Safe engineer to resolve this issue.
No Flow Thermistor Fault (L3): The L3 fault code indicates a configuration issue with the Printed Circuit Board (PCB). Contact a Gas Safe engineer to resolve this technical issue.
Overheating (L9/H9/HA/LA):
These fault codes indicate overheating due to excessive pressure. Try bleeding your radiators to rectify the issue. If the problem persists, contact a Gas Safe engineer for further assistance.
Boiler Fails to Ignite (LF): The LF code indicates that your boiler is not igniting. Press the reset button for 2–5 seconds to resolve this issue. If the problem persists, check other gas appliances and contact a Gas Safe engineer.
Boiler Return Pipe Problem (L5): The L5 code indicates that the boiler has been restarted too many times. Turn off the boiler completely and restart it to check if it functions correctly. If not, contact a Gas Safe engineer.
“Flame Detection Fault (“L6): The L6 code indicates a flame detection fault. Reset the boiler to resolve the issue. If the problem persists, contact the manufacturer for assistance.
Boiler Chip Card Fault (C2): The C2 fault code indicates an error with the boiler chip card. Reset the boiler and if the problem continues, contact a Gas Safe engineer.
Central Heating Signal Problem (C0): The C0 code indicates a problem with central heating signals, likely caused by the circulating pump or thermostat. Contact a Gas Safe engineer to resolve this issue.
No Display: If there is no display on your Ideal boiler, it suggests a fault in the Printed Circuit Board (PCB). Turn off the boiler, restart it, and if the problem persists, contact a qualified professional for assistance.
Noisy boiler: Unusual noises such as kettling, vibrating, or humming are common in boilers. Check for loose components or try repressurizing the boiler to stop the noise. If the issue persists, seek further assistance.
Fault Code 0: When your Ideal boiler displays fault code 0, it means the boiler is in standby mode, waiting for a request for hot water or central heating.
Remember, if you encounter any of these fault codes, it’s essential to consult a qualified professional, such as a Gas Safe engineer or the manufacturer’s technical support, for accurate diagnosis and resolution. They have the expertise to ensure the safe and efficient operation of your Ideal boiler.
If you encounter any of these fault codes on your Ideal boiler, it is recommended to seek professional assistance from a qualified heating engineer or the manufacturer’s technical support. They have the expertise to diagnose and resolve boiler issues effectively and safely, ensuring the optimal functioning of your heating system.
Ariston Boiler Fault Codes
A01: No flame detection.
A03: Ignition fault.
A12: Low water pressure.
A40: Fan fault.
A44: Faulty temperature sensor.
Alpha Boiler Fault Codes
E10: Ignition fault.
E28: Flame loss during operation.
E40: Low water pressure.
E78: Faulty temperature sensor.
E94: PCB fault.
Please note that this is not an exhaustive list of fault codes, and the meanings may vary depending on the specific boiler model and version. Always refer to your boiler’s user manual or manufacturer’s documentation for accurate information about fault codes associated with your particular boiler.
If you encounter a fault code on your boiler and are unsure how to proceed, it is highly recommended to contact a qualified heating engineer or the manufacturer’s technical support for assistance. They have the expertise to diagnose and resolve boiler issues safely and efficiently.
Regular boiler maintenance and servicing can help prevent many common faults. It is advisable to have your boiler serviced annually by a Gas Safe registered engineer to ensure its optimal performance, improve energy efficiency, and reduce the likelihood of encountering fault codes.
Remember, addressing boiler faults promptly not only ensures your comfort but also prolongs the lifespan of your boiler and maintains a safe and efficient heating system in your home.
