A Vaillant fault code tells you why the boiler has stopped or locked out. Some, such as low pressure or a frozen condensate pipe, you can safely check yourself; most others need a Gas Safe registered engineer. Find your code below. Vaillant boilers show an F code, for example F.22 or F.28. Vaillant advises that you never open the boiler casing and that a reset may only clear a fault temporarily.
Smell gas, or a carbon monoxide alarm is sounding? Do not reset the boiler. Open windows, turn off the gas at the meter if it is safe to do so, leave the building and call the free gas emergency line on 0800 111 999. What to do →
Vaillant fault codes and what to do
F.22You may be able to fix this
What it means: Low water pressure in the system.
What to do: If the gauge reads below 1 bar, Vaillant says a competent person may repressurise using the filling loop. If it keeps dropping, call an engineer.
F.28You may be able to fix this
What it means: The flame was not detected during ignition: the boiler failed to light.
What to do: Check other gas appliances, your prepayment meter credit and that the condensate pipe outside is not frozen. If none of these fixes it, call an engineer.
F.29You may be able to fix this
What it means: The flame went out during operation and the boiler could not relight.
What to do: Same checks as F.28: gas supply, meter credit and frozen condensate pipe. Then call an engineer.
F.54You may be able to fix this
What it means: Fault in the gas supply (shown with F.28 or F.29).
What to do: Check your gas supply and prepayment meter credit. If gas is fine elsewhere, call an engineer.
F.75You may be able to fix this
What it means: No pressure change was detected when the pump started (Vaillant groups it with the same pressure advice as F.22).
What to do: Vaillant gives the same advice as F.22: check and top up the pressure if below 1 bar, otherwise call an engineer.
F.20You may be able to fix this
What it means: The safety thermal cut-out has operated and shut the boiler off (overheat).
What to do: Check the pressure, look for leaks, make sure radiator valves are open and bleed any trapped air. If it returns, call your installer.
F.27Engineer needed
What it means: A flame signal was detected while the burner is off.
What to do: Vaillant says this is for an expert only. Do not attempt it yourself.
F.32Engineer needed
What it means: Fan fault.
What to do: Needs a Gas Safe engineer.
F.35Engineer needed
What it means: The air or flue pipe is blocked.
What to do: Switch the boiler off and call an engineer or your installer.
F.0 / F.1Engineer needed
What it means: The flow (F.0) or return (F.1) temperature sensor has been interrupted.
What to do: Needs an engineer.
F.83You may be able to fix this
What it means: When the burner starts, little or no temperature rise is registered at the flow or return sensor.
What to do: Vaillant advises contacting your installer. Checking the pressure gauge first is still worthwhile.
F.88Engineer needed
What it means: The electrical connection to the gas valve has been interrupted.
What to do: Needs a Gas Safe engineer.