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Vaillant boiler fault codes

A Vaillant boiler

If your Vaillant boiler is displaying a code beginning with the letter F, then it is signalling that the appliance is experiencing a fault. To help fix your Vaillant boiler fault code, have a look below

Jump to:

F.49
F.52
F.53
F.54
F.56
F.57
F.61
F.62
F.63
F.64
F.65
F.67
F.68
F.70
F.71
F.72
F.73
F.74
F.75
F.76
F.77
F.78
F.83
F.84
F.85
F.92
F.93


Vaillant boiler fault codes

F.49: eBUS fault

Short circuit on the eBUS, eBUS overload or two power supplies with different polarities on the eBUS.

F.52: Mass flow sensor connection fault

Mass flow sensor not connected/disconnected, plug not connected or incorrectly connected or an issue with its operation.

F.53: Mass flow sensor fault

Mass flow sensor faulty, filter below venturi filter cap wet or blocked, gas flow pressure too low.

F.54: Gas pressure fault (in combination with F.28/F.29)

No or too little gas supply pressure, gas valve closed.

F.56: Fault – Mass flow sensor regulation

Gas valve defective, cable harness to gas valve defective.

F.57: Fault during comfort safety mode

Ignition electrode is highly corroded.

F.61: Fault – Gas valve regulation

  • Short circuit/short to earth in cable harness for the gas valve
  • Gas valve defective (coils shorted to earth)
  • Defective electronics

F.62: Fault – Gas valve switch-off delay

  • Delayed shutdown of gas valve
  • Delayed extinguishing of flame signal
  • Gas valve leaking
  • Defective electronics

F.63: EEPROM error

Defective electronics

F.64: Electronics/NTC fault

Supply or return NTC short circuited, electronics defective.

F.65: Electronic temperature fault

Electronics overheating due to external influences

F.67: Electronics/flame fault

Implausible flame signal, electronics defective.

F.68: Unstable flame signal fault

This could be caused by:

  • Air in gas
  • Gas flow pressure too low
  • Incorrect air ratio
  • condensate route blocked
  • Wrong gas restrictor
  • Ionisation flow interruption (cables, electrodes)
  • Flue gas recirculation
  • Condensate route

F.70: Invalid device specific number (DSN)

Spare part case: Display and PCB replaced at same time and DSN not set, wrong or missing output range coding resistor.

F.71: Flow NTC fault

Flow temperature sensor signalling constant value:

  • Flow temperature sensor incorrectly positioned at supply pipe
  • Flow temperature sensor defective

F.72: Flow/return NTC fault

Flow/return NTC temperature difference too great → flow and/or return temperature sensor defective.

F.73: Water pressure sensor signal in the wrong range (too low)

  • Interruption/short circuit of water pressure sensor
  • Interruption/short circuit to GND in the supply line to water pressure sensor or water pressure sensor defective

F.74: Water pressure sensor signal outside the correct range (too low)

Cable to water pressure sensor has short-circuited at 5V/24 V or internal fault in water pressure sensor.

F.75: Fault, no pressure change detection when starting pump

  • Water pressure sensor and/or pump defective
  • Air in heating installation
  • Water pressure too low in boiler; check the pressure gauge and repressurise to 1 bar if needed

F.76: Overheating protection on primary heat exchanger has responded

Cable or cable connections for safety fuse in primary heat exchanger or primary heat exchanger defective.

F.77: Flue non-return flap/condensate pump fault

No response from flue non-return flap or condensate pump defective.

F.78: Interruption to DHW outlet sensor at external controller

UK link box is connected, but the hot water NTC is not bridged.

F.83: Flow and/or return temperature sensor temperature change fault

  • When the burner starts, the temperature change registered at flow and/or return temperature sensor is non-existent or too small
  • Not enough water in the boiler
  • Flow and/or return temperature sensor not in correct position at pipe

F.84: Fault – Flow/return temperature sensor difference implausible

  • Flow and return temperature sensors return implausible values
  • Flow and return temperature sensors have been inverted
  • Flow and return temperature sensors have not been correctly fitted

F.85: Fault – Flow and return temperature sensors incorrectly fitted

Flow and/or return temperature sensors have been fitted to the same pipe/wrong pipe.

F.92: Coding resistor fault

The coding resistor on the PCB does not match the entered gas family. Check the resistor, repeat the gas family check and enter the correct gas family.

F.93: Gas group fault

Combustion quality outside the permitted range: Wrong gas restrictor, recirculation, wrong gas family, internal pressure measuring point in venturi blocked (do not use lubricant on O-ring in venturi.). Gas family check prematurely terminated.

Communication fault

No communication with PCB.

Vaillant boiler repairs from HomeServe

Experiencing problems with your Vaillant boiler? Our expert repairs team are on hand to diagnose the issue and will aim to get things working again in no time.

Alternatively, if you’re looking for a new boiler, we’re working together with BOXT, one of the largest boiler installation companies in the UK, to help you find the best boiler for your home.

BOXT makes choosing the perfect new boiler for your home easy with a fixed price quote on your screen in just 90 seconds.

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About the author

Yasmin Gray became a qualified plumber in 2008 and now works as a service excellence coach at HomeServe. She joined HomeServe in 2018.

Yasmin specialises in plumbing and works for HomeServe as a service excellence coach, coaching the South and West London teams.

She chose HomeServe because: “It is a great place to work as a female engineer.”

Qualifications

Team leader level 3, Unvented, Electrics for plumbers, IOSH Health and Safety.

Years qualified

Since 2008.

The perfect brew

“Strong with a dash of milk. Oh and with the tea bag left inside the cup!”
Read more

Share this post

About the author

Yasmin Gray became a qualified plumber in 2008 and now works as a service excellence coach at HomeServe. She joined HomeServe in 2018.

Yasmin specialises in plumbing and works for HomeServe as a service excellence coach, coaching the South and West London teams.

She chose HomeServe because: “It is a great place to work as a female engineer.”

Qualifications

Team leader level 3, Unvented, Electrics for plumbers, IOSH Health and Safety.

Years qualified

Since 2008.

The perfect brew

“Strong with a dash of milk. Oh and with the tea bag left inside the cup!”
Read more

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