Medium
bA on Viessmann Vitodens 100-W WB1A

Your boiler is struggling to talk to the specific controller that helps manage heating in different zones of your home, which may result in radiators in certain areas not warming up correctly.

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.

What the manual says

Manufacturer manual

Communication fault - extension kit for mixer circuit M2

From this model's manual
Verified against the Viessmann Vitodens 100 W Wb1a installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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