Low
d.23 on Vaillant ecoTEC Plus 630

Your boiler is simply reporting that it is currently set to standby mode and is not being asked to provide heating or hot water.

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

Status of the heating demand: off=Heating off (Summer mode), on=Heating on

From this model's manual
Verified against the Vaillant Ecotec Plus 615 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 boiler control panel to ensure the heating is switched to 'On'Increase the target temperature on your room thermostat to be higher than the current room temperatureEnsure the central heating timer or programmer is currently set within an 'On' period

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