BoilerFaultCodesVaillant S.15 Fault Code
Also written as S15 — same fault.
The Vaillant S.15 fault code means: your boiler is simply finishing a safety cooling cycle after you have finished using hot water, and there is no cause for concern.. It appears on 36 Vaillant models in our database.
Technical description: DHWmode:Pump/fanoverrun
What causes the Vaillant S.15 fault?
This status occurs as the boiler completes a safety sequence to confirm that the internal pump is circulating water properly and the fan is operating at the correct speed. It is a normal part of the start-up process where the system verifies all conditions are safe before allowing the burner to ignite. If the code stays on screen too long, it may suggest a slight delay in the pump or fan reaching their required operating levels.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the S.15 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax
- Combi Compact 242EB
- Combi Compact 282EB
- Combicompact vcw282eh
- ecoFIT Pure 435
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoMAX Repair: £150-350
- Ecomax Condensing 600/800 series Repair: £150-300
- ecoTEC
- ecoTEC exclusive
- ecoTEC exclusive 627
- ecoTEC plus
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC plus 637
- ecoTEC Plus 826
- ecoTEC Plus 832
- ecoTEC Plus 836
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus aquaPLUS
- ecoTEC Pro
- ecoTEC Pro / ecoTEC Plus
- ecoTEC Pro 24
- ecoTEC Pro 28
- ecoTEC Pro 30
- ecoTEC sustain
- Home Combi
- Home System
Source
Vaillant S.15 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant Combicompact vcw282eh manual (PDF)
- Vaillant Combi Compact 282EB manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026