BoilerFaultCodesVaillant F.077 Fault Code
Also written as F077 — same fault.
The Vaillant F.077 fault code means: your boiler has detected an issue with the drainage system or flue safety mechanism, so it has safely stopped working to prevent potential water damage or combustion faults.. It appears on 3 Vaillant models in our database.
Technical description: A condensate pump or an external flue non-return flap is blocking the burner operation.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the F.077 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F.077 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026