High
F.77 on Glow-worm 38cxi

Your boiler has detected a blockage in the drainage system or an issue with the flue, causing it to shut down to prevent water or exhaust gases from backing up.

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

Fault: Condensate or smoke

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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Related fault codes

F.28View →F.29View →

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