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Vaillant Fault Codes

Welcome to the fault-codes section of this site. The following table or page contains the information required to help repair and diagnose the fault codes being shown on the boiler display. You may be guided through the fault finding sequence or steps, for rectifying your boiler with this fault code. Suggested repair solutions may be provided by a link to a repair page. NB Some fault codes are only applicable to a specific range of boilers only.

Brand Specific Information

Fault codes take priority over all other display functions in the event of a system fault occurring. If multiple faults occur, the corresponding fault codes are displayed alternately for about two seconds each. Shown below is the procedure to access fault code history for most digital Vaillant boilers.

Fault Memory

Older Ecotecs
8.1.4 Fault memory

The fault memory stores details of the ten most recent faults.

• Press the ”i” and ”–” buttons simultaneously.

• Use the ”+” button to scroll back through the list of memorised errors. To cancel fault error memory display mode, proceed as follows:

• Press the ”i” button below the display or

• Do not touch any key for about four minutes. The display will now revert back to showing the current flow temperature.

New Ecotecs

  • Access through the digital menu
F.00LinkFlow temperature sensor interruptionNTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC defective
F.01LinkReturn temperature sensor interruptionNTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC defective
F.02LinkInterruption cylinder charging sensor actoSTOR (NTC) only in combination with F.91NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on actoSTOR electronics
F.03LinkInterruption cylinder sensor actoSTOR (NTC) only in combination with F.91NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on actoSTOR electronics
F.10LinkFlow NTC short circuiNTC defective, short circuit in cable harness, cable/casing
F.11LinkReturn NTC short circuitNTC defective, short circuit in cable harness, cable/casing
F.12LinkShort circuit at cylinder charging sensor (NTC) only in combination with F.91NTC defective, short circuit in cable harness, cable/casing
F.13Link VU-/VUW boiler: Short circuit warm start sensor/
cylinder sensor
VUW boiler with actoSTOR: Short circuit cylinder
sensor (NTC) only in combination with F.91
NTC defective, short circuit in cable harness, cable/casing
F.20LinkSafety switch-off: temperature limiterIncorrect earth connection between cable harness and boiler, flow or
return NTC defective (loose connection), black discharge via ignition
cable, ignition plug or ignition electrode
F.22LinkSafety switch-off: low water pressureNo or to low water pressure in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective
F.23LinkSafety switch-off: Temperature difference too greatPump blocked, insufficient pump output, air in boiler, flow and return NTC interchanged
F.24LinkSafety switch-off: Temperature rise too fastPump blocked, poor pump performance, air in boiler, system pressure too low, non-return valve blocks/incorrectly installed
F.25LinkSafety switch-off: Flue gas temperature too highBreak in plug connection for optional flue gas safety thermostat (STB), break in cable harness
F.26LinkFault: Gas valve without functionGas 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
F.27LinkSafety switch-off: Flame simulationMoisture on the electronics, electronics (flame monitor) defective, gas solenoid valve leaking
F.28LinkFailure during start-up: ignition unsuccessfulGas meter defective or gas pressure regulator has triggered, air in gas,
gas flow pressure too low, thermal isolator device (TAE) has triggered,
condensate duct blocked, incorrect gas restrictor, incorrect ET gas valve,
fault on the gas valve, multiple plug on PCB incorrectly plugged in, break
in cable harness, ignition system (ignition transformer, ignition cable,
ignition plug, ignition electrode) defective, ionisation current interrupted
(cable, electrode), incorrect earthing of boiler, electronics defective
F.29LinkFailure during operation: Re-ignition unsuccessfulGas supply temporarily stopped, flue gas recirculation, condensate duct
blocked, faulty earthing of boiler, ignition transformer has spark failure
F.32LinkFan FaultPlug at fan not correctly plugged in, multiple plug on PCB not correctly plugged in, break in cable harness, fan blocked, Hall sensor defective, electronics defective
F.35LinkAir/flue gas duct faultAir/flue gas duct blocked
F.42LinkCoding resistor fault (possible in combination with F.70)Short circuit/interruption in coding resistor output range (in cable harness
at heat exchanger) or gas group resistor (on PCB)
F.49LinkeBUS faultShort circuit on the eBUS, eBUS overload or two power supplies with different polarities on the eBUS
F.52LinkMass flow sensor connection faultMass flow sensor not connected/disconnected, plug not connected or incorrectly connected
F.53LinkMass flow sensor faultMass flow sensor faulty, filter below venturi filter cap wet or blocked, gas flow pressure too low
F.54LinkGas pressure fault (in combination with F.28/F.29)No or too little gas supply pressure, gas valve closed
F.56LinkFault: Mass flow sensor regulationGas valve defective, cable harness to gas valve defective
F.57LinkFault during comfort safety modeIgnition electrode highly corroded
F.61LinkFault: Gas valve regulationShort circuit/short to earth in cable harness for the gas valve Gas valve defective (coils shorted to earth) Electronic defective
F.62LinkFault: Gas valve switch-off delayDelayed shutdown of gas valve Delayed extinguishing of flame signal Gas valve leaking Electronics defective
F.63LinkEEPROM errorElectronics defective
F.64LinkElectronics/NTC faultSupply or return NTC short circuited, electronics defective
F.65LinkElectronic temperature faultElectronics overheating due to external influences, electronics defective
F.67LinkElectronics/flame faultImplausible flame signal, electronics defective
F.68LinkUnstable flame signal faultAir 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.70LinkInvalid 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.71LinkFlow NTC faultFlow temperature sensor signalling constant value:
-Flow temperature sensor incorrectly positioned at supply pipe
-Flow temperature sensor defective
F.72LinkFlow/return NTC faultFlow/return NTC temperature difference too great ÌÎå«_ÌÎÌ__ÌÎÌ_Ì´Ìö flow and/or return temperature sensor defective
F.73LinkWater 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.74LinkWater 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.75LinkFault, no pressure change detection when starting pumpWater 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.76LinkOverheating protection on primary heat exchanger has respondedCable or cable connections for safety fuse in primary heat exchanger or primary heat exchanger defective
F.77LinkFlue non-return flap/condensate pump faultNo response from flue non-return flap or condensate pump defective
F.78LinkInterruption to DHW outlet sensor at external controllerUK link box is connected, but hot water NTC not bridged
F.83LinkFlow and/or return temperature sesnsor temperature change faultWhen 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.84LinkFault: Flow/return temperature sensor difference implausibleFlow 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.85LinkFault: Flow and return temperature sensors incorrectly fittedFlow and/or return temperature sensors
have been fitted to the same pipe/wrong pipe
F.92LinkCoding resistor faultThe 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.93LinkGas group faultCombustion quality outside the permitted range: Wrong gas restrictor,
recirculation, wrong gas family, internal pressure measuring point in ven-
turi blocked (do not use lubricant on O-ring in venturi.). Gas family check
prematurely terminated.
ComLinkCommunication Fault;
No communication with PCB

3 thoughts on “Vaillant Fault Codes”

  1. Customer has a fault code come up F.83. once reset button with the fire symbol and it turned on boiler this has now happened a couple of times what could be the reason

    1. Hi,

      You if fault F83, you likely have some sort of blockage in the system, that is not allowing the return water temperature to warm up, or you have a faulty return sensor which is less likely.


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