High
S.42 on Vaillant ecoTEC Pro 30

Your boiler has detected a blockage or communication error in its venting system, which is preventing it from safely starting 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

Flue non-return flap return signal blocks burner operation (only in connection with VR 40 accessories) or condensate pump faulty, heat requirement is blocked

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.22View →

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