High
F.77 on Vaillant ecoTEC plus Regular

Your boiler is having trouble draining away the water it creates during normal operation, or it is sensing an issue with the exhaust air system.

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

Condensate pump or flue gas non-return flap fault

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.22View →F.25View →

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