Medium
F.78 on Vaillant ecoTEC exclusive

Your boiler is struggling because it has detected an external control unit connected for hot water, but the required safety link or sensor connection is missing.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Interrupt.:DHWoutletsensoronext.contr. UKlinkboxisconnectedbutthedomestichotwaterNTCisnotbridged

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.77View →F.73View →

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