D.074 Low

Vaillant D.074 Fault Code

Also written as D074 — same fault.

The Vaillant D.074 fault code means: your boiler is currently running a routine high-temperature cycle designed to kill bacteria in your hot water storage tank, which is a normal part of its maintenance program.. 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: actoSTOR anti-legionella function

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.074 fault code

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

Source

Vaillant D.074 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