BoilerFaultCodesVaillant 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 31 Vaillant models in our database.
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.
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
Find a Gas Safe engineer
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A cover plan would handle faults like S.24: no call-out fees, no surprise bills.
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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.
- ecoFIT Pure 412
- ecoFIT Pure 418
- ecoFIT Pure 425
- ecoFIT Pure 435
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835
- ecoMAX
- ecoMAX 613
- ecoMAX 618
- ecoMAX 622
- ecoMAX 635
- ecoMAX 824/2 E
- ecoMAX 828/2 E
- ecoMAX 835 E
- Ecomax Condensing 600/800 series
- ecoTEC exclusive
- ecoTEC plus Repair: £0-120
- ecoTEC plus VU GB 656/4-5 A
- ecoTEC pro
- ecoTEC sustain
- Home Combi 25
- Home Combi 30
- Home Combi 35
- Turbomax 824/828
- Turbomax Plus
- Turbomax Plus 824/828E
- Turbomax Plus 828
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
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.
- Vaillant ecoFIT Pure 425 manual (PDF)
- Vaillant ecoFIT Pure 435 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026