High
F.77 on Vaillant ecoTEC Plus 826

Your boiler has detected an issue with an external accessory, such as the condensate drainage pump or the ventilation system, which is preventing it from running safely.

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

Accessory fault (flue non-return flap, condensate pump, etc.)

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.75View →

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