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Vaillant Boiler Fault Codes

Kentish Plumbers are here to help.

We know it's frustrating when your boiler displays an error code, which is why we've listed some common boiler error codes below. If you're still stuck, do give us a call on 01892 489771 or click here to email us and one of our team will be able to assist.

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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

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

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

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

Short circuit: Flow sensor: NTC defective, short circuit in cable harness, cable/casing

Short circuit: Return sensor: NTC defective, short circuit in cable harness, cable/casing

Short circuit: DHW outlet sensor: Only in conjunction with F.91NTC defective, short circuit in cable harness, cable/casing

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

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

Safety switch-off: Low water pressure: No or insufficient water in the product, water pressure sensor defective

Safety switch-off: Temp.spread too large: Pump blocked, insufficient pump output, air in product, flow and return NTC connected the wrong way round

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

Safety switch-off: Flue temp. too high: Break in plug connection for optional flue gas safety temperature limiter (STB), break in cable harness

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

Safety switch-off: Flame simulation: Moisture on the electronics, electronics (flame monitor) defective, gas solenoid valve leaking

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

Start-up failure: Ignit. unsuccessful: Gas supply temporarily stopped, flue gas recirculation, condensate duct blocked, defective earthing of product, ignition transformer has spark failure

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

Fault: eBUS: Short circuit on eBUS, eBUS overload or two power supplies with differ- ent polarities on the eBUS

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

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.

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

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

Fault: Measuring program: Active comfort protection mode has detected a regulation fault– Ignition electrode highly corroded

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

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

Fault: EEPROM: Electronics defective

Fault: Electronics/sensor: Flow or return NTC short circuited, electronics defective

Fault: Electronics temp.: Electronics overheating due to external influences, electronics defective

Fault: Electronics/flame: Implausible flame signal, electronics defective

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

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

Fault: Flow sensor: Flow temperature sensor signalling constant value:– Flow temperature sensor incorrectly positioned at supply pipe– Flow temperature sensor defective

Fault: Flow/return sensor: Flow/return NTC temperature difference too great → flow and/or returntemperature sensor defective

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

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

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

Fault: Flue non-ret. valve/condens. pump: No response from flue non-return flap or condensate pump defective

Interrupt.: DHW outlet sensor on ext. contr: UK link box is connected but the hot water NTC is not bridged

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 electronics Sensor plug has short to earth to the casing, short circuit in cable har-ness, sensor defective

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

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

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

Fault: NTCs fitted incorrectly: The flow and/or return temperature sensors have been installed on the same pipe/incorrect pipe

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.

Sensor/actuator fault on actoSTOR module

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

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.

actoSTOR electronics status: LED on: Communication OKLED flashing: Communication not OK LED off: No power supply

Communication fault: Communication fault between display and PCB in the electronics box

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