Low
d.66 on Vaillant Home System

This is a settings status message indicating whether your boiler's pre-heat feature for hot water is currently switched on or off.

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 Home System 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

Navigate to the 'd.66' menu setting in the installer level or diagnostic menu.Change the value to '1' (on) if you want instant hot water, or '0' (off) to save energy.Press the 'Menu' or 'Tick' button to save the setting.

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d.67View →d.70View →

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