BoilerFaultCodesVaillant S.15 Fault Code
Also written as S15 — same fault.
The Vaillant S.15 fault code means: your boiler is performing a self-check to ensure water is moving correctly and the fan is working before it attempts to ignite.. It appears on 26 Vaillant models in our database.
Technical description: Fan and water pump return water
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.
DIY fix possible
No action is required as this is a normal status message, not a permanent error.Wait 5-10 minutes for the boiler to complete its internal system check.Ensure your radiator valves are open to allow water to circulate properly during the check.
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Gas Safe Register →Vaillant models that show the S.15 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS
- Atmomax
- Combi Compact 242EB
- Combi Compact 282EB
- ecoTEC
- ecoTEC exclusive
- ecoTEC plus
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 65
- ecoTEC Plus 832
- ecoTEC Plus 836
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus Aquaplus
- ecoTEC plus System
- ecoTEC Pro
- ecoTEC Pro / ecoTEC Plus
- ecoTEC Pro 24
- ecoTEC Pro 28
- ecoTEC Pro 30
- ecoTEC sustain
- 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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026