D.22 Low

Vaillant D.22 Fault Code

Also written as D22 — same fault.

The Vaillant D.22 fault code means: your boiler is currently preparing or delivering hot water, which is a normal operating status of the pre-heat function rather than a failure.. It appears on 28 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: Check diagnostic code. (turboMAX Plus only) check diverter valve spindle against blade lightly. Replace diverter valve.

What causes the Vaillant D.22 fault?

This status occurs when the boiler's internal pre-heat function, known as Warmstart, is active to ensure hot water is available quickly. It is triggered either by the boiler periodically heating its own internal store or when you turn on a hot water tap. This is part of the appliance's normal operation and indicates the system is working as intended to maintain comfort.

DIY fix possible

Check if the hot water tap is currently runningTurn off the 'Warmstart' comfort function using the dial if you do not want the boiler to fire periodically to keep water hotMonitor the display to see if it switches back to a heating or standby code once the demand ends

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Vaillant models that show the D.22 fault code

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

Source

Vaillant D.22 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 27 April 2026