Boiler Fault Codes from all Leading Manufacturers
When there’s a fault with your boiler, an error code will generally be displayed on the front panel to help you figure out what the problem is, it also helps gas engineers like us to quickly diagnose and rectify issues.
A fault code can mean anything from a simple fix to a significant and potentially dangerous problem with the boiler, so it’s really important to report any error codes to a professional.
If your boiler is displaying a fault code, you can find out what it means using our boiler code tool below, use the search function for quick and easy locating
| Code | Manufacturer | Meaning |
|---|---|---|
| 9A | Worcester Bosch | Boiler has been fitted with incorrect Heat Control Module (HTM). |
| 9U | Worcester Bosch | Faulty or not properly connected code plug. |
| B7 | Worcester Bosch | Control board needs replacing. |
| C6 | Worcester Bosch | System is running too fast or slow. |
| C7 | Worcester Bosch | Fan is not running or the airflow is blocked. |
| D1 | Worcester Bosch | Sensor has become wet, damaged or has disconnected. Boiler will block for 300 seconds. |
| D1 | Worcester Bosch | Boiler is overheating. |
| E2 | Worcester Bosch | Flow sensor has shorted, become damaged or has disconnected. |
| E5 | Worcester Bosch | Primary flow sensor has overheated. |
| E9 | Worcester Bosch | Main heat exchanger has overheated. |
| E9 | Worcester Bosch | Max temperature sensor has failed or can't be recognised. |
| EA | Worcester Bosch | Flue gas thermostat has overheated. |
| EA | Worcester Bosch | Boiler has failed to ignite 4 times. Boiler will wait 30 seconds before another attempt is made. |
| EA | Worcester Bosch | Flame has been extinguished due to moisture in sump, blocked sump or wind in flue. |
| EA | Worcester Bosch | Gas valve coil has disconnected. |
| EA | Worcester Bosch | Flame has not extinguished within 4 seconds of ignition. |
| EA | Worcester Bosch | Pump is not detecting water. |
| F.00 | Vaillant | Interruption: Flow sensor: NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC defective |
| F.01 | Vaillant | Interruption: Return sensor: NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC defective |
| F.02 | Vaillant | Interruption: DHW outlet sensor: Only in conjunction with F.91NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on the actoSTOR electronics |
| F.03 | Vaillant | Interruption: Cylinder sensor: Only in conjunction with F.91NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on the actoSTOR electronics |
| F.10 | Vaillant | Short circuit: Flow sensor: NTC defective, short circuit in cable harness, cable/casing |
| F.11 | Vaillant | Short circuit: Return sensor: NTC defective, short circuit in cable harness, cable/casing |
| F.12 | Vaillant | Short circuit: DHW outlet sensor: Only in conjunction with F.91NTC defective, short circuit in cable harness, cable/casing |
| F.13 | Vaillant | Short circuit: Cylinder sensor: Combination product: Warm start sensor/cylinder sensor short circuitCombination product with actoSTOR: Short circuit cylinder sensor (NTC) only in combination with F.91NTC defective, short circuit in cable harness, cable/casing |
| F.20 | Vaillant | Safety switch-off: Temperature limiter: Incorrect earth connection between cable harness and product, flow or return NTC defective (loose connection), black discharge via ignition cable, ignition plug or ignition electrode |
| F.22 | Vaillant | Safety switch-off: Low water pressure: No or insufficient water in the product, water pressure sensor defective, |
| F.23 | Vaillant | Safety switch-off: Temp.spread too large: Pump blocked, insufficient pump output, air in product, flow and return NTC connected the wrong way round |
| F.24 | Vaillant | Safety switch-off: Temp. incr. too fast: Pump blocked, insufficient pump output, air in product, system pressure too low, non-return valve blocked/incorrectly installed |
| F.25 | Vaillant | Safety switch-off: Flue temp. too high: Break in plug connection for optional flue gas safety temperature limiter (STB), break in cable harness |
| F.26 | Vaillant | Fault: Fuel valve not working: Gas valve stepper motor not connected, multiple plug on the PCB not plugged in correctly, interruption in cable harness, gas valve stepper motor defective, electronics defective |
| F.27 | Vaillant | Safety switch-off: Flame simulation: Moisture on the electronics, electronics (flame monitor) defective, gas solenoid valve leaking |
| F.28 | Vaillant | Start-up failure: Ignit. unsuccessful: Gas meter defective or gas pressure monitor has triggered, air in gas, gas flow pressure too low, thermal isolator device (TAE) has triggered, condensate duct blocked, incorrect gas restrictor, incorrect spare part gas valve, value in D.052 does not correspond to the printed value on the current gas valve, fault on the gas valve, multiple plug on PCB incor- rectly plugged in, break in cable harness, ignition system (ignition trans- former, ignition cable, ignition plug, ignition electrode) defective, ionisa- tion current interrupted (cable, electrode), incorrect earthing of product, electronics defective |
| F.29 | Vaillant | Start-up failure: Ignit. unsuccessful: Gas supply temporarily stopped, flue gas recirculation, condensate duct blocked, defective earthing of product, ignition transformer has spark failure |
| F.32 | Vaillant | Fault: Fan: 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.49 | Vaillant | Fault: eBUS: Short circuit on eBUS, eBUS overload or two power supplies with different polarities on the eBUS |
| F.52 | Vaillant | Contact fault mass flow sensor/Venturi: The mass flow sensor/Venturi is not connected electrically – The plug is not plugged in correctly – The plug is not plugged in – The plug is defective – The slot is defective (loose connection) – Mass flow sensor/Venturi defective |
| F.53 | Vaillant | Combustion regulation fault: The combustion regulation has detected a fault – Gas flow pressure too low – Liquid gas coding resistance used when operating with natural gas – If the fault occurs again after being cleared: – Gas valve defective – Mass flow sensor/Venturi defective, wet or blocked (if the fault occurs again after being cleared): Do not wet the sensor, do not use any lubricants on the O-ring on the Venturi. |
| F.54 | Vaillant | Fault in the gas supply (in combination with F.28/F.29): There is insufficient gas supply to operate the unit – Gas isolator cock(s) closed – Gas flow pressure is too low – Gas valve defective |
| F.56 | Vaillant | Safety switch-off: CO limit exceeded: Safety switch-off: CO limit exceededA component in the combustion regulation is defective– Contact fault at the gas valve (plug not plugged in correctly or not plugged in, plug defective, slot is defective (loose connection))– If the fault occurs again after being cleared: The gas valve is defective |
| F.57 | Vaillant | Fault: Measuring program: Active comfort protection mode has detected a regulation fault– Ignition electrode highly corroded |
| F.61 | Vaillant | Fault: Fuel valve actuation: The gas valve cannot be actuated– Cable harness supply line to the gas valve is defective (short to earth, short circuit)– Gas valve defective– PCB defective |
| F.62 | Vaillant | Fault: Fuel valve switch-off delay: Delayed shutdown of gas valve detected– Secondary light (ignition and monitoring electrode indicates delayed extinguishing of the flame signal)– Gas valve defective– PCB defective |
| F.63 | Vaillant | Fault: EEPROM: Electronics defective |
| F.64 | Vaillant | Fault: Electronics/sensor: Flow or return NTC short circuited, electronics defective |
| F.65 | Vaillant | Fault: Electronics temp.: Electronics overheating due to external influences, electronics defective |
| F.67 | Vaillant | Fault: Electronics/flame: Implausible flame signal, electronics defective |
| F.68 | Vaillant | Fault: Flame signal unstable: Air in gas, gas flow pressure too low, incorrect air ratio, condensate duct blocked, ionisation flow interruption (cable, electrode), flue gas recirculation, condensate duct |
| F.70 | Vaillant | Fault: Invalid Device Specific Number: If spare parts fitted: Display and PCB replaced at same time and DSN not reset, incorrect or missing output range coding resistance |
| F.71 | Vaillant | Fault: Flow sensor: Flow temperature sensor signalling constant value:– Flow temperature sensor incorrectly positioned at supply pipe– Flow temperature sensor defective |
| F.72 | Vaillant | Fault: Flow/return sensor: Flow/return NTC temperature difference too great → flow and/or returntemperature sensor defective |
| F.73 | Vaillant | Fault: Water press. sensor: Interruption/short circuit of water pressure sensor, interruption/short circuit to GND in supply line to water pressure sensor or water pressure sensor defective |
| F.74 | Vaillant | Fault: Water press. sensor: The line to the water pressure sensor has a short circuit to 5 V/24 V or internal fault in the water pressure sensor |
| F.75 | Vaillant | Fault: Pump/ water shortage: Water pressure sensor and/or pump defective, air in the heating installa- tion, insufficient water in the product; connect external expansion vessel to the return |
| F.77 | Vaillant | Fault: Flue non-ret. valve/condens. pump: No response from flue non-return flap or condensate pump defective |
| F.78 | Vaillant | Interrupt.: DHW outlet sensor on ext. contr: UK link box is connected but the hot water NTC is not bridged |
| F.80 | Vaillant | Fault: actoSTOR inlet sensor: Only in conjunction with F.91NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on the actoSTOR electronicsSensor plug has short to earth to the casing, short circuit in cable har- ness, sensor defective |
| F.81 | Vaillant | Fault: cylinder charging pump: Only in conjunction with F.91Cylinder is not fully charged after specified time.– Check cylinder charging sensor and cylinder sensor– Air in the actoSTOR pump– Inspect cable harness for pump– Check the impeller sensor and/or limiter in the product– Diverter valve defective– Secondary heat exchanger blocked– Pump faulty |
| F.83 | Vaillant | Fault: NTC temp. gradient: When the burner starts, the temperature change registered at the flow and/or return temperature sensor is non-existent or too small.– Insufficient water in product– Flow or return temperature sensor not in correct position at pipe |
| F.84 | Vaillant | Fault: NTC temp. diff. implausible: Flow and return temperature sensors returning implausible values.– Flow and return temperature sensors have been inverted– Flow and return temperature sensors have not been correctly in-stalled |
| F.85 | Vaillant | Fault: NTCs fitted incorrectly: The flow and/or return temperature sensors have been installed on the same pipe/incorrect pipe |
| F.90 | Vaillant | Fault: Communication: Check the cable harness from the product to the actoSTOR module (PEBus).If the product is to be operated without an actoSTOR module, setD.092 = 0. |
| F.91 | Vaillant | Sensor/actuator fault on actoSTOR module |
| F.92 | Vaillant | Coding resistance fault: The coding resistance on the PCB does not match the entered gas group: Check the resistance, repeat the gas family check and enter the correct gas group |
| F.93 | Vaillant | Poor combustion quality: Combustion regulation has detected poor combustion quality– Incorrect gas restrictor has been installed for the gas family (anothergas family is present)– Recirculation– Mass flow sensor/Venturi defective (wet, blocked): Do not wet thesensor, do not use any lubricants on the O-ring on the Venturi. |
| LEDactoSTOR module | Vaillant | actoSTOR electronics status: LED on: Communication OKLED flashing: Communication not OK LED off: No power supply |
| Err | Vaillant | Communication fault: Communication fault between display and PCB in the electronics box |
Worcester Bosch Boiler Fault Codes
Worcester Bosch is one of the leading boiler brands in the UK. At Home Assist 365, we are Worcester Bosch accredited installers meaning we have the skills and training to fix all common faults with Worcester Boilers.
Vaillant Boiler Fault Codes
Vaillant is another leading UK boiler manufacturer with global coverage. At Home Assist 365, we are Vaillant accredited installers and so customers can be assured that we have the training and expertise to fix all faults with any model of Vaillant boiler.
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