Common Boiler Fault Codes
From time to time, issues can arise with your boiler, and when one does, most modern boilers are designed to display a fault (error) code on screen. These boiler fault codes tell you what the problem is and what might be causing it.
Understanding what each of these boiler fault codes is telling you can make your life a lot easier. If you find yourself in a position where you require boiler servicing and repairs, a quick call to MJ Burt on 01202 721955, and we’ll be round to put things right.
Alternatively, if your boiler has reached the end of its life, we can supply and install a new boiler for you that’s both reliable and energy efficient.
Ariston Boiler Fault Codes
- 101 All Boilers Overheat
- 102 E-Combi Evo
- E-System Evo
- Clas He Evo (Combi and system) Pressure sensor error
- 103 All Boilers Insufficient circulation
- 104 All Boilers Insufficient circulation
- 105 All Boilers Insufficient circulation
- 106 All Boilers Insufficient circulation
- 107 All Boilers Insufficient circulation
- 108 All Combi Boilers Insufficient water (request filling)
- 109 Clas net one / Clas one Combi
- Clas system one System pressure greater than 3 bar
- 110 All Boilers Central heating Flow temperature probe circuit open / short circuit
- 112 All Boilers Central heating return temperature probe circuit open / short circuit
- 114 All Boilers External sensor circuit open / short circuit
- 116 All Combi and System Boilers Floor thermostat contact open
- 118 All Boilers Heating delivery probe problem
- 1p1 All Boilers Insufficient circulation indication
- 1p2 All Boilers Insufficient circulation indication
- 1p3 All Boilers Insufficient circulation indication
- 1p4 Clas Net one Combi
- Clas one Combi
- Clas System one Insufficient circulation indication
- 301 All Boilers EEPROM error
- 302 All Boilers Communication error
- 303 All Boilers Main printed circuit board (PCB) error
- 304 All Boilers Too many resets (> 5) in 15 minutes
- 305 All Boilers Main printed circuit board (PCB) error
- 306 All Boilers Main printed circuit board (PCB) error
- 307 All Boilers Main printed circuit board (PCB) error
- 3P9 E-combi one
- E-System one
- Clas Net one Combi
- Clas one Combi
- Clas System one Schedule service
Glow-worm Boiler Fault Codes
- F.00: Flow temperature sensor – NTC plug not plugged in or has come loose, multiple plugs on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective
- F.01: Return temperature sensor – NTC plug not plugged in or has come loose, multiple plugs 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 via ignition 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 to 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 – Break in 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: 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 plugs on PCB incorrectly plugged in, break in cable harness, ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective, ionisation current interrupted (cable, electrode), incorrect earthing of product. electronics defective
- F.29: 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 plugs 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: Gas valve control system – Short circuit/short to earth in cable harness for the gas valve, gas valve defective (coils shorted to earth), electronics defective
- F.82: Gas valve switch-off control – Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas valve leaking, electronics defective
- F.83: EEPROM – Electronics defective
- F.64: Electronics/sensor/analogue-to-digital converter – Flow or return NTC short circuited, electronics defective
- F.85: Electronics temperature too high – Electronics overheating due to external influences, electronics defective
- F.67: Value sent back by ASIC is incorrect (flame slgnal) – Implausible flame signal, electronics defective
- F.88: Unstable flame (analogue input) – Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas restricter, 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: Flow/return temperature sensor – Flow temperature sensor signalling constant value: Flow temperature sensor incorrectly positioned on supply pipe, flow temperature sensor defective
- F.72: 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: Water pressure sensor not connected or has short-circuited – 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: 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: 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: 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: 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: 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: 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: Underfloor heating contact – Underfloor heating contact open, sensor disconnected or defective
- F.87: Electrodes – Electrodes not connected or they are connected incorrectly, short circuit in the cable harness
- F.88: Gas valve – Gas valve not connected or it is connected incorrectly, short circuit in the cable harness
- F.89: Pump – Pump not connected or it is connected incorrectly, incorrect pump connected, short circuit in the cable harness
- Connection: No communication between the PCB and the user interface, electronics defective
Vaillant Boiler Fault Codes
- F.0: The flow temperature sensor has been interrupted – Fault in the electrical connection for the flow temperature sensor or flow temperature sensor defective
- F.1: The return temperature sensor has been interrupted – Fault in the electrical connection for the return temperature sensor or return temperature sensor defective
- F.10: The flow temperature sensor has short-circuited – Fault in the electrical connection for the flow temperature sensor or flow temperature sensor defective
- F.11: The return temperature sensor has short-circuited – Fault in the electrical connection for the return temperature sensor. Return temperature sensor defective.
- F.12: The domestic hot water connection temperature sensor has short-circuited – Fault in the electrical connection for the domestic hot water temperature sensor. Domestic hot water temperature sensor defective.
- F.13: The cylinder temperature sensor has short-circuited – Fault in the electrical connection for the cylinder temperature sensor. Cylinder temperature sensor defective
- F.20: The safety thermal cut out has operated shutting the boiler off – System water pressure below normal range of 1 to 1.5 bar, fault in the electrical connection for the flow and/or return temperature sensor, flow and/or return temperature sensor defective, circulation fault, pump, valve, blockage, water pressure sensor defective, volume flow sensor defective, ignition cable, ignition plug or ignition electrode
- F.22: Low water pressure in the system – The water pressure in your system is below the normal range of 1 to 1.5 bar, a problem with the water pressure sensor, Loose, disconnected, or faulty wiring for the pump or pressure sensor, water pressure sensor faulty, the pump may not be working properly (Open vented boilers only), or internal expansion vessel faulty
- F.23: The temperature spread between the flow/return is too great – Air in the product, fault in the electrical connection for the flow and/or return temperature sensor, flow and/or return temperature sensor defective, circulation fault, pump, valve, blockage, or internal expansion vessel defective
- F.24: The temperature increases too quickly – Air in the product, system pressure too low, fault in the electrical connection for the flow and/or return temperature sensor, flow and/or return temperature sensor defective, circulation fault, pump, valve, blockage, or internal expansion vessel defective
- F.25: The flue gas temperature is too high – Circulation fault, pump, valve, blockage, wiring harness defective, or flue gas temperature monitor has triggered
- F.27: A flame signal has been detected while the burner is off – Gas solenoid valve not leaktight or PCB defective
- F.28: The flame signal was not detected during the ignition phase – Not enough gas reaching the boiler (for example, low gas pressure or insufficient credit on a pre-payment meter, condensate has backed up in the combustion chamber due to a blocked condensate pipe, the ignition electrode may be faulty, the PCB (circuit board) could be faulty, or there may be an issue with the flue system.
- F.29: The ignition following a flame loss during operation was unsuccessful – The gas supply is interrupted, insufficient gas pressure, fault in the flue gas route caused by recirculation or flue gas blockage, poor electrical earthing, condensate discharge pipe blocked, or control electrode got contact with the burner
- F.32: Fan fault – Fan defective, plug or harness defective, or PCB issue
- F.35: The air/ flue pipe is blocked – Gas flow pressure too low, fault in the flue gas route caused by recirculation or flue gas blockage, condensate discharge pipe blocked, insufficient combustion air supply, or control electrode defective
- F.52: Mass flow sensor fault – The mass flow sensor/Venturi is not connected electrically, the plug is defective/not plugged in, the slot is defective (loose connection), mass flow sensor/Venturi defective
- F.53: Combustion regulation fault – The combustion regulation has detected a fault, gas pressure too low, incorrect coding resistor used when operating with natural gas, gas valve defective, filter below Venturi blocked, mass flow sensor defective
- F.54: 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, or gas valve defective
- F.57: The boiler is not burning correctly in comfort mode – Fault in the flue, recirculation of flue products, condensate discharge pipe blocked, gas pressure too low, cable harness damaged or defective, PCB defective, fan defective
- F.62: The flame switch-off was detected after a delay – Gas valve defective, PCB defective, ignition electrode defective
- F.70: The Device Specific Number (DSN) is incorrect, missing or does not match the coding resistor – Device Specific Number not set / is incorrect, or interruption in the cable harness
- F.72: The temperature spread between the flow and return temperature sensor is invalid – Flow and/or return temperature sensor defective, or circulation fault, pump, valve, blockage
- F.75: The pressure change is too low when the heat pump is started up – System pressure below normal range of 1 to 1.5 bar, air in the product/heating system, water pressure sensor defective, internal heating pump defective, or open circuit in cable harness
- F.83: When the burner starts, little or no temperature increase is registered at the flow or return temperature sensor – System pressure too low, circulation fault, pump, valve, blockage, or flow/return temperature sensor fault
- F.84: The temperature differences between the flow and return temperature sensors return implausible values – Flow and return pipe work crossed, circulation fault, pump, valve, blockage, or flow and return temperature sensors incorrectly fitted or on the wrong pipe
- F.88: The electrical connection to the gas valve has been interrupted – Gas valve assembly connected incorrectly or short circuit in the cable harness
