Low
d.21 on Vaillant ecoFIT Pure 435

Your boiler is simply indicating that the 'warm start' feature, which keeps water hot for faster taps, is currently active.

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 warm start for hot water

From this model's manual
Verified against the Vaillant Ecofit Pure 830 installation & service manual, page 30.
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

This is a status code, not a fault; no repair is needed.If you wish to stop the boiler from firing periodically, locate the 'Warmstart' button on your boiler control panel.Press the button to toggle the feature off if you prefer to save energy.

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