BoilerFaultCodesVaillant S.10 Fault Code
Also written as S10 — same fault.
The Vaillant S.10 fault code means: your boiler is simply letting you know that it has detected you have turned on a hot tap and it is currently working to heat your water.. It appears on 26 Vaillant models in our database.
Technical description: DHW demand. The domestic hot water demand is activated.
What causes the Vaillant S.10 fault?
This code appears when the boiler recognizes that a hot water tap or shower has been opened somewhere in your home. It occurs because a flow sensor has detected moving water and has signaled the internal components to begin the heating process. It is a normal part of the boiler's operation and simply confirms that the system is responding correctly to your request for hot water.
DIY fix possible
No action is required as this is a normal status message, not a fault.If the code stays on when all taps are off, check for dripping taps or leaks.If the code appears but no hot water comes out, contact a Gas Safe engineer.
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A cover plan would handle faults like S.10: no call-out fees, no surprise bills.
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Vaillant models that show the S.10 fault code
Click a model for the full fault code list and model-specific repair notes.
- 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
- 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.10 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 835 manual (PDF)
- Vaillant Ecomax Condensing 600/800 series manual (PDF)
- Vaillant ecoMAX 835 E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026