High
F5/F9 on Viessmann Vitodens 100-W

Your boiler is failing to start because it cannot detect that the internal fan, which clears exhaust gases, is spinning correctly.

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.

Technical description

Fan starts fault: Checking fan cables and plugs

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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