Call us on 03300 585917 from Monday to Friday 09:00AM to 5:00PM or email us on

Vaillant Boiler Error codes

//Vaillant Boiler Error codes

Vaillant Boiler Faults / Error codes

Like any boiler, Vaillant boiler could develop a fault. We have prepared this guide to help you understand vaillant boiler fault and error codes. You might be able to resolve some of your boiler issues but it is recommend to contact a gas safe engineer if your boiler keep developing faults. If your Vaillant boiler is in warranty then you can call Vaillant technical team to help you understand or resolve vaillant boiler faults.

         Error Codes / Faults                                                                  Cause

F.00 / F.0Flow temperature sensor interruption
F.01 / F.1Return temperature sensor interruption
F.10Flow NTC short circuit
F.11Return NTC short circuit
F.20Safety switch off- temperature limiter
F.22Safety switch off – low water pressure
F.23Safety switch off temperature difference too great
F.24Safety switch off temperature is rising to fast
F.25Safety switch off flue gas temperature too high
F.26Error with gas valve – possible no function
F.27Safety switch off flame simulation
F.28Failure during start up – ignition unsuccessful to start
F.29Failure during operation – re-ignition unsuccessful
F.32Fan error
F.49eBUS error – possible short circuit
F.61Fault with gas valve regulation – Short circuit or faulty Gas valve.
F.62Gas valve switch off delay – Gas valve leaking, Delayed shutdown of Gas valve.
 F.63EEPROM error – Electronics fault.
 F.64Electronics / NTC error – Supply / return NTC short circuited
F.65Electronic temperature error – Electronics could be overheating due to external influences
F.67Electronics flame error – Faulty Flame, Electronics fault
F.68Unstable flame signal error – Air in gas, Gas flow pressure issue. Flue issues
F.70Invalid device specific number (DSN)
F.71Flow NTC error code – flow temperature sensor signalling constant value, Flow temperature sensor issue
F.72Flow return NTC error – temperature difference too great, Defective sensor
F.73Water pressure sensor signal in the wrong range –Pressure sensor or water pressure sensor defective
F.74Water pressure sensor signal outside correct range – Internal fault in water pressure sensor
F.75No pressure change detection when starting the pump– Water pressure sensor faulty, Low water pressure
F.76Overheating protection on primary heat exchanger has responded – Primary heat exchanger defective
F.77Flue non return flap condensate pump error – Faulty condensate pump
F.78Interruption to DHW outlet sensor at external controller – Hot water NTC not bridged
F.83Flow and or return temperature sensor error – Not enough water in the boiler, Faulty flow or return sensors
F.84Error with flow or return temperature sensor temperature changing error – Faulty sensors or issue with sensors
F.85Error with flow and return temperature – Temperature sensors  incorrectly fitted
Communication FaultNo communication with the PCB

       Error Codes / Faults                                                                  Cause

Central Heating Mode
S.00Heating mode error – no heat required
S.01Fan pre-run
S.02Pump pre-run
S.03Ignition error
S.04Burner on
 S.06Fan overrun
 S.07Pump overrun
S.08Anti cycling period
Domestic Hot water mode
S.10Domestic hot water demand
S11Fan pre-run
S.13Ignition error
S.14Burner on
S.15Pump or Fan overrun
S.16Fan overrun
S.17Pump overrun
Preheat mode
S.20Domestic hot water cycling mode active
S.21Fan pre heat
S.22Pump pre run error
S.23Ignition error
S.24Burner error
S.25Pump / fan overrun
S.26Fan overrun
S.27Pump overrun
S.28Anti-cycling period
S.30No heating demand from external controls
S.31No heat demand- boiler in summer mode
S.32Antifreeze active- Fan speed variation too high
S.34Frost protection active
S.39Condensate pump error
S.40Comfort safety mode active
S.41Water pressure > 2.8 bar
S.42Accessory module is blocking burner operation
S.46Comfort safety mode flame loss at minimum load
S.53Waiting time, Temperature difference flow
S.54Waiting time – No water in system pressure
S.57Waiting period comfort safety mode
S.58Modulation limitation, Noise / wind error
S.61Gas check unsuccessful

This is a very common fault in Vaillant ecoTec models. There are a number of causes for this error and sometime could be tricky to diagnose. We have listed some of the most common causes below to help you

  • Water pressure sensor defective
  • Pump defective
  • Air in central heating installations
  • Low pressure in the boiler

A gas engineer will be able to diagnose the boiler fault.


Use our free service to get boiler quotes and save money on boiler replacement.. Gas safe