Low
d.17 on Vaillant Home System

Your boiler has been adjusted to measure the temperature of the water returning from your radiators rather than leaving the boiler, which is a standard setting often used for underfloor heating systems.

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

Heating control: off=Flow temperature, on=Return temperature (adjustment for underfloor heating)

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.17' setting in the installer level menuChange the value from 1 (Return) to 0 (Flow) if you do not have underfloor heatingPress the 'Menu' or 'M' button to save the setting and exit

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