BoilerFaultCodesVaillant S.13 Fault Code
Also written as S13 — same fault.
The Vaillant S.13 fault code means: your boiler is currently trying to light the flame to provide hot water for your taps or shower.. It appears on 42 Vaillant models in our database.
Technical description: DHW mode: Ignition. The ignition for domestic hot water mode is activated.
What causes the Vaillant S.13 fault?
This isn't actually a fault, but a status message indicating that you have turned on a hot tap and the boiler is starting its ignition process. It occurs because the internal sensor has detected water flow and is now sparking the burner to heat that water for your shower or sink. If the code stays on screen without the water getting hot, it may suggest an issue with the gas supply or the ignition electrodes.
DIY fix possible
This fault may be fixable without an engineer. Check your manual first.
Find a Gas Safe engineer
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Vaillant models that show the S.13 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 435
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoMAX Repair: £120-250
- ecoMAX 613
- ecoMAX 618
- ecoMAX 622
- ecoMAX 635
- Ecomax Condensing 600/800 series
- ecoMAX System 612
- ecoTEC
- ecoTEC exclusive
- ecoTEC exclusive 627
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 826 Repair: £120-250
- ecoTEC Plus 832
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus aquaPLUS
- ecoTEC Pro
- ecoTEC Pro / ecoTEC Plus
- ecoTEC Pro 24
- ecoTEC Pro 28
- ecoTEC Pro 30 Repair: £120-250
- ecoTEC sustain
- Home Combi
- Home System
- Thermocompact
- Turbomax 824/828 Repair: £100-250
- Turbomax Plus Repair: £100-250
- Turbomax Plus 824/828E Repair: £120-250
- Turbomax Plus 828 Repair: £0-120
- Turbomax Plus 828 E Repair: £120-250
- Turbomax Plus VUW 242E Repair: £120-250
- Turbomax Plus VUW 242EH Repair: £120-250
Source
Vaillant S.13 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 ecoFIT sustain 630 manual (PDF)
- Vaillant Ecomax Condensing 600/800 series manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026