High
F0b on Viessmann Vitodens 025-W

Your boiler has detected an electrical fault with the internal sensor that monitors water temperature, meaning it cannot safely regulate heat and has shut down.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Short circuit, flow temperature sensor heat generator circuit (dual sensor)

From this model's manual
Verified against the Viessmann Vitodens 025 W installation & service manual, page 61.
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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F0aView →F0cView →F02View →

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