UK & Europe
Vaillant error codes
Vaillant ecoTEC gas boilers show a fault as the letter F and a number, written with a dot: F.22 or F.28. The newest ecoTEC plus boilers add a zero, so F.28 becomes F.028. aroTHERM plus heat pumps use three-digit codes such as F.723 on the VWZ AI control module. The codes and their meanings here come from Vaillant's UK fault code list and its ecoTEC and aroTHERM plus manuals.
- 28 codes
- Boilers & Heat pumps
- Checked against official pages
Boilers 16 codes
F22 Low water pressure
The water pressure in your heating system has dropped too low, so the boiler has shut down for now.
F28 No flame detected when lighting
The boiler tried to light but didn't detect a flame, so it has locked out.
F29 Flame went out and won't relight
The flame went out while the boiler was running, and it couldn't light again.
F75 No pressure rise when the pump starts
When the boiler's pump started, the pressure didn't change as much as it should.
F20 Overheat: safety cut-out tripped
The flow or return water temperature went over the maximum limit, so the safety cut-out has shut off the gas valve.
F23 Flow and return temperatures too far apart
The water leaving the boiler is much hotter than the water coming back to it.
F27 Flame detected with the burner off
The boiler sensed a flame when the burner should have been off.
F62 Flame went out too slowly
When the boiler shut off the gas, it detected the flame going out later than it should have.
F00 Flow temperature sensor fault
The boiler can't get a proper reading from the sensor that measures the water leaving it, so it has stopped for safety.
F01 Return temperature sensor fault
The boiler can't get a proper reading from the sensor on the return, the water coming back from the radiators, so it has stopped.
F24 Temperature rising too fast
The water in the boiler heated up too quickly, usually because it isn't circulating properly, so the boiler shut down to protect itself.
F25 Flue gas temperature too high
The exhaust gases are too hot, or the flue gas safety circuit has been broken, so the boiler has shut down for safety.
F32 Fan speed fault
The boiler's fan isn't running at the speed it should, so the boiler has stopped.
F61 Gas valve control fault
The boiler's control electronics can't operate the gas valve the way they should, so it has shut down.
F63 Control board memory (EEPROM) fault
The boiler's control board has found a fault in its memory, so the boiler won't run.
F83 Not enough water when the burner lit
When the burner lit, the boiler's temperature sensors saw almost no change.
Heat pumps 12 codes
F022 Heating water pressure too low
The water pressure in your heating system, which Vaillant calls the building circuit, has fallen below 0.5 bar for more than a minute.
F723 Pressure too low, heat pump switched off
The water pressure in the heating system has fallen below the minimum, so the heat pump has switched itself off automatically.
F788 Heating circuit pump fault
The heating pump's own electronics have found a problem, such as running dry, a blockage or a voltage fault, and have switched the pump off and locked it.
F718 Outdoor unit fan blocked
The heat pump has had no signal that the fan in the outdoor unit is turning.
F733 Evaporation temperature too low
The refrigerant in the outdoor unit is getting too cold.
F741 Return water too cold during defrost
While the outdoor unit was defrosting, the water coming back from your heating system dropped below 13 °C.
F731 High-pressure switch open
The refrigerant pressure in the outdoor unit got too high, so the built-in high-pressure safety switch has tripped.
F752 Frequency converter (inverter) fault
The frequency converter, the electronics that drive the compressor, has reported a fault.
F1117 Compressor phase failure
The heat pump has found a problem with the power supply to the compressor, such as a blown fuse, low mains voltage or a supply that is not connected.
F514 Compressor inlet temperature sensor fault
The heat pump is not getting a usable reading from the temperature sensor at the compressor inlet.
F546 High-pressure sensor fault
The heat pump is not getting a usable reading from the refrigerant high-pressure sensor.
F585 Outlet temperature sensor fault (refrigerant)
The heat pump is not getting a usable reading from one of the temperature sensors in its refrigerant circuit, most likely the one at the condenser outlet.
No codes of that type for this brand.
Good to know
- Resetting: on older ecoTEC plus and ecoTEC pro boilers, press the fault clearance key for one second. The 2023 ecoTEC plus manual says to hold the reset button for more than three seconds. Vaillant's manuals allow three attempts at most.
- If the boiler doesn't come back on after a reset, or the code is still there, Vaillant says to call a Gas Safe registered engineer. Needing to reset it regularly isn't normal either.
- Pressure: Vaillant's ecoTEC plus and ecoTEC pro manuals ask for 1.0 to 2.0 bar with the system cold.
- If you smell gas, leave the property straight away and call the National Gas Emergency Service on 0800 111 999.
- aroTHERM plus heat pumps: Vaillant's installation instructions say to press the reset button once the cause has been dealt with. If the fault keeps coming back after several resets, contact Vaillant Customer Service or your installer.
- aroTHERM plus heat pumps: Depending on the fault, Vaillant says the system can keep heating or making hot water with reduced comfort (limp-home mode) until it is repaired.
Official help pages
- Vaillant: boiler fault codes list
- Vaillant: understanding an F28 fault code
- Vaillant: how to thaw a frozen boiler condensate pipe
- Vaillant: what to do if your boiler has no pressure
Every code page links the exact pages it was checked against. Last reviewed October 2026.
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344 codes from 24 brands, each one checked against the maker's own manuals and support pages.