BoilerFaultCodesVaillant S.05 Fault Code
Also written as S05 — same fault.
The Vaillant S.05 fault code means: your boiler is currently cooling itself down after a period of operation, which is a normal process and not actually a fault code.. It appears on 42 Vaillant models in our database.
Technical description: Fan and pump over run (837/637 only)
What causes the Vaillant S.05 fault?
This status occurs because your boiler needs to move heat away from its internal components after it has finished heating your home or hot water. The fan and pump continue to run for a short time to safely vent residual heat and prevent the unit from overheating. Once the internal temperature has dropped to a safe level, the boiler will return to its normal standby mode.
DIY fix possible
Wait for approximately 5 to 10 minutes for the cycle to complete.Ensure your room thermostat or programmer is calling for heat if the boiler does not restart.Check that your radiator valves are open to allow heat to dissipate.
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Vaillant models that show the S.05 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 exclusive 627
- 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 630
- ecoTEC Plus 635
- ecoTEC Plus 826
- 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
- ecoTEC sustain
- Home Combi
- Home System
- Thermocompact
- 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.05 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