F.684 Emergency

Viessmann F.684 Fault Code

Also written as F684 — same fault.

The Viessmann F.684 fault code means: your boiler has detected an issue with the air flow or exhaust system, meaning it has safely shut down to prevent unsafe gases from building up inside your home.. It appears on 2 Viessmann models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: Burner in a fault state. Back draught safety device faulty.
Typical repair cost £150-350 (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 F.684: 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 F.684 fault code

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

Source

Viessmann F.684 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