d.85 Low

Vaillant d.85 Fault Code

Also written as D85 — same fault.

The Vaillant d.85 fault code means: your boiler has detected that it is unable to run at its lowest power setting, which may cause it to perform slightly less efficiently or cycle on and off more frequently than usual.. It appears on 8 Vaillant models in our database.

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.

Technical description: Increase in the min. output (heating and hot water handling mode)
Typical repair cost £120-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the d.85 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant d.85 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026