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 problem, have a look below at each fault code:
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)
- 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
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-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, 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 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.
No communication with PCB.
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