Emergency
D.118 (6) on Vaillant ecoTEC exclusive

Your boiler has detected an internal sensor fault that could affect the accuracy of its air-quality monitoring, meaning it has safely shut down to prevent incorrect operation.

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 resistance measurement not OK

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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