Emergency
D.118 (4) on Vaillant ecoTEC exclusive

Your boiler has detected an inconsistency in how it monitors heat levels, causing it to shut down for safety reasons.

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: Heater temperature plausibility check 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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