Smell gas? Leave the property and call the National Gas Emergency line on 0800 111 999

Viessmann fault code

Viessmann F8: fuel valve closes too late

Engineer only

The gas valve took too long to close. This needs an engineer to check the gas valve.

What you can safely do

There is nothing you can safely do yourself with this one. Leave the boiler off and book an engineer.

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.

From Viessmann's own fault tables. Your model name is usually on the front of the boiler or in the user manual.

Model	Meaning	Causes listed for engineers
Vitodens 100-W (B1HC/B1KC)	Fuel valve closes too late	Check gas train and both control paths

Can I use the boiler with F8?

No. Leave it off and book a Gas Safe registered engineer.