Medium Warning
76:1 on Viessmann Vitodens 333-F

Your boiler is having difficulty communicating with its internal smart connection module, usually meaning there is a minor electronic glitch or a connection has come loose.

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

With LON communication module; automatic recognition

What causes this fault?

This fault occurs when the boiler's internal brain loses touch with the communication module that allows it to talk to other smart devices or controls. It is usually caused by a loose connection following a recent service, or a small electronic failure where the internal wiring has become insecure. In some cases, it simply means the communication board has failed and needs replacing to restore the data link.

DIY fix possible

Switch off the power to the boiler at the main isolation switchWait for 30 seconds before switching the power back onPress the 'Reset' button on the control panelIf the fault persists, book a qualified heating engineer

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