Medium
b4 on Viessmann Vitodens 343-F WS4A

Your boiler is still running, but its internal controls are working as if it is much colder outside than it really is, so it may heat your home less efficiently and less accurately than normal.

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

Regulates as if the outside temperature was 0 °C. Cause: Internal fault.

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 343 F Ws4a 5592883 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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Related fault codes

F16View →F17View →

All 59 fault codes on the Vitodens 343-F WS4A

Seeing a different code? Every code this model can display, in one place.

0F9A9b9C9F10182028303840485058929394A6A7b0b1b5b7b8bAbCbdbEbFC2CdCECFdAdbdddEE4E5E8E9EAEbECEdF0F1F2F3F4F8F9FAFCFdFEFF

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