BoilerFaultCodesVaillant S.108 Fault Code
Also written as S108 — same fault.
The Vaillant S.108 fault code means: your boiler is currently performing a routine self-cleaning cycle to clear any fumes from the system before it attempts to ignite.. It appears on 23 Vaillant models in our database.
Technical description: Purgingthecombustionchamber,faninoperation
What causes the Vaillant S.108 fault?
This status occurs when the boiler detects a need to clear the internal combustion area of any residual gases or debris before it can safely start the burner. It is a natural part of the boiler's safety protocol, triggered by the fan spinning at high speed to ensure a clean environment for ignition. This cycle is usually temporary and does not signify that a component has failed.
DIY fix possible
Wait for the process to complete, as this is a normal status message and not a breakdownEnsure there are no obstructions around the external flue pipe outside your homeIf the code persists for several minutes without the boiler firing up, try resetting the boiler once
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Vaillant models that show the S.108 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
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoTEC plus 412
- ecoTEC plus 415
- ecoTEC plus 418
- ecoTEC plus 424
- ecoTEC plus 430
- ecoTEC Plus 610
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 635
- ecoTEC Plus 840
- ecoTEC sustain
- Home Combi
- Home System
Source
Vaillant S.108 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 835 manual (PDF)
- Vaillant ecoFIT sustain 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026