Medium
F.78 on Vaillant Home System

Your boiler is having trouble communicating with the hot water sensor in your external control box, meaning your hot water may not reach the desired temperature.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

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

InterruptiontoDHWoutletsensoratexternalcontroller Linkboxconnected,buthotwaterNTCnotbridged

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.13View →

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