D.025 Low

Vaillant D.025 Fault Code

Also written as D025 — same fault.

The Vaillant D.025 fault code means: your boiler is currently receiving a signal from your room thermostat or controller to heat your water, and it is simply showing you that this function is active.. It appears on 7 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: Hot water generation enabled by eBUS controller

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.025 fault code

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

Source

Vaillant D.025 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