Low
d.66 on Vaillant ecoTEC sustain

This code simply confirms whether your boiler is currently set to keep a small amount of water pre-heated for faster hot water taps, rather than indicating a fault.

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

Activation of the warm start function for hot water: off=Function deactivated, on=Function activated

From this model's manual
Verified against the Vaillant Ecotec Sustain installation & service manual, page 49.
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

Locate the menu button on your boiler displayNavigate to the 'Comfort' or 'Warmstart' settingSelect 'on' if you want faster hot water, or 'off' to save on energy costs

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