S.24 Low

Vaillant S.24 Fault Code

Also written as S24 — same fault.

The Vaillant S.24 fault code means: your boiler is temporarily reducing its power because it has reached the required temperature and is waiting for the heat to be distributed before firing up again normally.. It appears on 43 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 burner holding operation on / Cylinder charging burner on

What causes the Vaillant S.24 fault?

This occurs when your boiler has heated the water to the target temperature so quickly that the heat hasn't had enough time to circulate through your radiators or hot water cylinder. To prevent overheating, the boiler temporarily lowers its flame or pauses until the water temperature inside the unit drops to a level where it can safely start heating again. It is often a sign that the pump is moving water slowly or your radiators are struggling to dissipate the heat.

This is more common during the autumn and spring when your heating is turned on but the weather is mild, meaning your home requires less heat than the boiler’s minimum output.

Typical repair cost £0-120 (including labour)

DIY fix possible

Check that at least one radiator with a manual valve is turned fully openEnsure your Thermostatic Radiator Valves (TRVs) are not all set to 'zero' or 'frost'Wait 10-15 minutes to see if the status changes as the water cools down

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Vaillant models that show the S.24 fault code

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

Source

Vaillant S.24 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