High
S.42 on Vaillant Combi Compact 242EB

Your boiler has paused operation because a safety flap in the flue system is stuck or sending an incorrect signal, preventing waste gases from being cleared 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

Flue non return flap return signal blocks burner operation

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

S.41View →F.32View →

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