Low
I.56 on Viessmann Vitodens 100-W WB1A

Your boiler is currently receiving a signal from an external device, such as a thermostat or heating controller, telling it to run.

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

External demand active

From this model's manual
Verified against the Viessmann Vitodens 100 W Wb1a 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

Check your room thermostat or smart heating controller to see if it is actively calling for heatAdjust the target temperature on your thermostat to ensure it is not set higher than the room temperatureVerify that your external heating timer or programmer is not currently set to 'On' or 'Boost' mode

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