Vaillant Boiler Fault Codes & Common Errors

Is there an issue with your Vaillant boiler? If you see a fault code displayed on your boiler then don't panic, the solution may not be as costly as you first assume. A lot of boiler errors can simply be fixed by a reset.

To help you out we have compiled a list of all the Vaillant boiler error codes and the potential issue that may have caused it. If you are stuck and can't find out what the problem is then we have help on hand with our partnered boiler engineer team who may be able to answer your queries remotely or send an engineer to take a look.

General Faults & Errors

This section is an overview of all of the types of errors that can occur on a Vaillant boilers.

Fault CodesDescriptionPotential Cause
F49Fault with eBUSShort circuit, overload or two power supplies with different polarities on the eBus
F52Fault with the mass flow sensor connectionThe plug for the mass flow sensor is not connected or has disconnected, it could have been incorrectly connected
F53Fault with mass flow sensorFaulty mass flow sensor

Wet or blocked filter below venturi filter cap

Pressure too low on gas flow
F54Fault with gas pressureThe gas valve may be closed or there is no / little gas supply pressure
F56Fault with the mass flow sensor regulationGas valve or the cable harness is defective
F57Fault during the comfort safety modeHighly corroded ignition electrode
F61Fault with the regulation of the gas valveDefective electronics or gas valve

Short circuit in cable harness of gas valve
F62Fault with the switch off delay of the gas valveGas valve delayed shut down

Delayed extinguishing of flame signal

Electronics defective or gas valve leaking
F63Error with EEPROMDefective electronics
F64Fault with electronics / NTCDefective electronics: supply or return NTC short circuited
F65Fault with electronic temperatureDefective electronics: overheating due to external influences
F67Fault with the electronics / flameDefective electronics: implausible flame signal
F68Fault with the flame signals (unstable)Air in gas

Wrong air ratio

Gas flow pressure too low

Condensate route blocked

Ionisation flow interruption

Wrong gas restrictor

F70Device specific number (DSN) invalidDisplay and PCB replaced at the same time and DSN not set
F71Fault with NTC flowFlow temperature sensor signalling constant value: incorrect positioned at supply pipe or defective
F72Fault with NTC flow / returnFlow / return NTC temperature difference too great or sensor defective
F73The water pressure sensor signal is in the wrong range as it's too lowInterruption / short circuit of water pressure sensor or defective sensor
F74Water pressure sensor signal outside correct range as it's too lowCable to water pressure sensor short circuited or fault with sensor
F75There is a fault due to no pressure change detection when pump startsDefective water pressure sensor and/or pump

Air in heating install

Low water pressure in boiler
F76Overheating protection on the primary heat exchangerDefective cable or cable connection for safety fuse in primary heat exchanger
F77Fault with the flue non-return flap / condensate pumpNo response from flue non return flap or condensate pump defect
F78Interruption to DHW outlet sensor at external controllerUK link box is connected but hot water NTC not bridged
F83Fault with the flow and/or return temperature sensorIncorrect position at pipe of the flow and / or return temperature sensor
F84Fault with the flow/return temperature sensor difference implausibleFlow and return temperature sensors return implausible values, the sensors have been inverted or not fitted correctly
F85Fault with the flow and return temperature sensors being incorrectly fittedWrong or the same pipe has been fitted with the flow and/or return temperature sensors
F92Fault with coding resistorThe error is due to the coding on the resistor on the PCB doesn't match the entered gas family. Check the resistor and repeat the check, then enter the gas family
F93Fault with group gasGas family check prematurely terminated

Combustion quality outside the permitted range: wrong gas restrictor or family, re circulation or internal pressure measuring point in venturi blocked.
Fault with communicationNo communication with printed circuit boardN/A