Low
A.12 on Viessmann Vitodens 200-W B2KF Combi

Your boiler's internal clock has lost its backup power, which means your timed heating schedules may be lost if there is a power cut.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Real time clock battery flat — replace CR2032 battery in HMU

From this model's manual
Verified against the Viessmann Vitodens 200 W B2kf Combi 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.

DIY fix possible

Locate the control panel at the front of the boiler.Carefully remove the small circular battery cover on the Heat Management Unit (HMU).Replace the old CR2032 coin battery with a new one, ensuring the '+' side faces outwards.Refit the cover and reset the time and date on the display menu.

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