F.20
Safety switch-off: overheating temperature reached
The boiler has shut down because an overheating safety threshold has been reached.
What this code means
The boiler has shut down because an overheating safety threshold has been reached.
Possible causes
- Flow or return NTC fault
- Poor circulation
- Electrical earthing or ignition-related interference
- Overheating condition
Common symptoms
- F.20 displayed
- Boiler locks out
- Heating/hot water stops
Checks to make
- Do not repeatedly reset an overheating boiler
- Check user-visible system pressure
- Arrange qualified diagnosis
Safety
- Do not remove the boiler casing or work on gas, combustion, flue or internal electrical components unless appropriately qualified. If gas is suspected, follow the national gas-emergency procedure.
Model notes
Vaillant notes that not every fault code is visible on every product model.