F4
Viessmann fault code
Viessmann F4: no flame signal
Check these first, then call an engineer
The burner didn't produce a flame signal, so the boiler has gone into a fault state. Viessmann's instructions list gas pressure, ignition parts and the condensate drain among the causes, and Viessmann says F4 is the code you're likely to see on a Vitodens when the condensate pipe has frozen.
What you can safely do
- Check your gas supply: turn on a gas hob or other gas appliance, as Viessmann suggests.
- In freezing weather, pour warm to hot (not boiling) water over the frozen part of the condensate pipe from a watering can or jug. If that isn't enough, try a hot water bottle.
- Reset the boiler as your manual describes.
Call a Gas Safe engineer if
- F4 comes back after these checks.
- You smell gas at any point. Leave the property and call 0800 111 999.
Find a Gas Safe engineer near you
Opens the official Gas Safe Register search.
Applies to: Vitodens 100-W (B1HC/B1KC). Codes can differ between models, so check your manual.