Medium
F.673 on Viessmann Vitodens 100-W WB1A

Your boiler is having trouble communicating with the solar water heating system, which means it cannot properly monitor or control the sun-heated water supply.

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

Thermostat function for solar control and solar transfer pump not working, Short circuit, temperature sensor, thermostat function TS3

From this model's manual
Verified against the Viessmann Vitodens 100 W Wb1a installation & service manual, page 99.
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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