Low
d.8 on Vaillant ecoMAX 635

Your boiler is simply indicating that your thermostat or external controller is currently requesting heat, which is a normal part of its standard operation.

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 controls heat demand

From this model's manual
Verified against the Vaillant Ecomax 613 installation & service manual, page 47.
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 controller settingsEnsure your heating programmer is set to your preferred scheduleNo physical intervention on the boiler is required as this is a status message

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Related fault codes

d.0View →d.1View →

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