Emergency
F.684 on Viessmann Vitodens 222-F B2TF

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

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

What the manual says

Manufacturer manual

Burner in a fault state. Back draught safety device faulty.

From this model's manual
Verified against the Viessmann Vitodens 222 F B2tf installation & service manual, page 107.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.685View →F.686View →

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