Medium
F.544 on Viessmann Vitodens 100-W WB1A

Your boiler is having trouble communicating with an external temperature sensor used for a second heating zone in your home, which may cause that specific area to be colder than intended.

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

Lead break, flow temperature sensor, heating circuit 2 with mixer

From this model's manual
Verified against the Viessmann Vitodens 100 W Wb1a installation & service manual, page 98.
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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