High
F.65 on Viessmann Vitodens 100-W WB1A

Your boiler is failing to light the fuel inside, meaning it cannot produce heat for your radiators or hot water taps.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

Flame signal is not present or insufficient at burner start.

From this model's manual
Verified against the Viessmann Vitodens 100 W Wb1a installation & service manual, page 85.
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 high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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