Medium Warning
77:1 on Viessmann Vitodens 222-W

Your boiler's internal communication system has detected an issue or a duplicate identity on its data network, which can sometimes happen after a power cut or part change.

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

LON user number

What causes this fault?

This fault occurs when the boiler's internal communication network becomes confused by seeing multiple components with the same identification number or when a signal is blocked. The most common reason is an electronic glitch following a power surge, or a conflict that arises after a technician has replaced a control board without reconfiguring its digital address.

DIY fix possible

Locate the 'Reset' button or menu option on the control panel.Perform a full system reset as per the user manual.Turn the power off at the fused spur switch for 30 seconds, then turn it back on.

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