Medium
F.669 on Viessmann Vitodens 100-W WB1A

Your boiler is having trouble communicating with the sensors that manage your hot water storage tank, which may lead to your hot water not heating 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

Preheating of second DHW cylinder and solar transfer pump not working, Short circuit, temperature sensor, DHW reheating TS4

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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