Emergency
D.118 (15) on Vaillant ecoTEC exclusive

Your boiler has detected an electrical issue with the built-in sensor that monitors combustion, meaning it cannot safely confirm the boiler is running correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description

CO sensor fault number: Reference voltage too low

Engineer required

This is a emergency 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.28View →F.29View →

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