Emergency
F3 on Viessmann Vitodens 343-F WS4A

Your boiler has detected a flame when it should not be burning, so it has stopped as a safety precaution and needs a qualified engineer to check the gas controls before it is used again.

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 - Flame signal is already present at burner start.

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 343 F Ws4a 5592883 installation & service manual.
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

F1View →F4View →

All 59 fault codes on the Vitodens 343-F WS4A

Seeing a different code? Every code this model can display, in one place.

0F9A9b9C9F10182028303840485058929394A6A7b0b1b4b5b7b8bAbCbdbEbFC2CdCECFdAdbdddEE4E5E8E9EAEbECEdF0F1F2F4F8F9FAFCFdFEFF

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