F8 High

Viessmann F8 Fault Code

The Viessmann F8 fault code means: your boiler has detected a problem with the gas valve not closing correctly, so it has shut down the burner for safety.. It appears on 9 Viessmann models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Burner in fault position. Fuel valve closes too late. Check the gas train and both control cables.

What causes the Viessmann F8 fault?

This fault occurs when the boiler's internal computer detects that the gas valve is taking too long to shut off or is failing to close completely after a heating cycle. The most common reason is a mechanical failure within the valve assembly itself or a communication error in the wiring harness that prevents the signal to close from being received instantly. For safety reasons, the boiler identifies this as a risk and prevents the burner from firing again until the issue is resolved.

Typical repair cost £250-450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like F8: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Viessmann models that show the F8 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Viessmann F8 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026