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Vaillant Boiler Problems: Fault Codes & Display Symbols

If your vaillant boiler is displaying a code beginning with F then it is signalling that the appliance is experiencing a fault. To help get your boiler up and running again, have a look below at each code and what fault it indicates.

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Code Meaning Cause
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
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 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)
  • Electronic defective
F.62 Fault: Gas valve switch-off delay
  • Delayed shutdown of gas valve
  • Delayed extinguishing of flame signal
  • Gas valve leaking Electronics defective
F.63 EEPROM error Electronics defective
F.64 Electronics/NTC fault Supply or return NTC short circuited, electronics defective
F.65 Electronic temperature fault Electronics overheating due to external influences, electronics defective
F.67 Electronics/flame fault Implausible flame signal, electronics defective
F.68 Unstable flame signal fault Air in gas, gas flow pressure too low, wrong 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 supply line to water pressure sensor or water pressure sensor defective
F.74 Water pressure sensor signal outside correct range (too low) Cable to water pressure sensor has short-circuitedd 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, too low water pressure in boiler; check adjustable bypass, connect external expansion vessel to return
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 hot water NTC not bridged
F.83 Flow and/or return temperature sesnsor temperature change fault
  • When the burner starts, the temperature change registered at flow and/or return temperature sensor is non-existant 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

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[28] Exclusions apply. See

[79] 5% online discount is available to domestic gas and LPG customers who receive an online quote for all boiler brands excluding the Ideal Logic HE24, HE30, HO15 & HO18 and Worcester Bosch 25i ERP, 30i ERP, 15ri & 18ri boilers which qualify for the winter bundles offer. £50 additional discount available on all like-for-like system swaps and a £100 additional discount is available on conventional to combi, and combi to conventional boiler swaps. Online discounted price is only available for the duration of the 14-day quote validity which starts from the day the quote was given. Help-Link UK Ltd include a filter as part of your quote as this is highly recommended by the boiler manufacturer as a key component in maintaining boiler health, functionality and may potentially be looked upon favourably by manufacturers when assessing warranty work. This filter can be removed at the customer's request. Quote also includes a programmable thermostat for all combi boiler installations as this is a legal requirement as part of the Boiler + legislation introduced 6th April 2018, and cannot be removed from the installation unless; it is replaced with an alternative smart thermostat; or another energy saving measure as listed in the Boiler + legislation or if a smart thermostat already exists within the property. Alternative thermostats, including smart thermostats are subject to an additional charge.

Customers within the following postcodes will be subject to regional price variations which will mean a premium is charged: BR, CR, DA, E, HA, EN, IG, KT, W, N, NW, RM, SE, SW, SM, TW, UB, WC, WD, EC

Offer is not available to Help-Link UK Ltd or HomeServe group employees. This offer cannot be used in conjunction with any other offers. Help-Link UK Ltd have the right to withdraw or change the offer at any time. Online discount is automatically applied when the customer gets a quote using the online quote system at and as long as the customer meets all the above criteria.