Low
D.23 on Vaillant ecoTEC 65kW

Your boiler is simply indicating its current operating mode, showing whether it is set to provide both heating and hot water or just 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

Summer/wintermode(heatingoff/on)

From this model's manual
Verified against the Vaillant Ecotec 65kw installation & service manual, page 31.
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 boiler control panel display to confirm the current mode settingsUse the mode button or menu settings on your boiler interface to switch between winter (heating and water) and summer (water only) modesConsult your user manual for the specific button sequence to adjust your heating schedule

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