BoilerFaultCodesVaillant S.08 Fault Code
Also written as S08 — same fault.
The Vaillant S.08 fault code means: your boiler is taking a short, normal break after finishing a heating cycle to prevent overheating and ensure everything cools down properly.. It appears on 43 Vaillant models in our database.
Technical description: Heatingmode:Temporaryshutdownafterheatingprocedure
What causes the Vaillant S.08 fault?
This occurs when the boiler has successfully met the temperature requested by your thermostat and shuts the burner off to prevent the system from getting too hot. It is a built-in safety delay that allows the internal components to cool down and the water to circulate before the boiler is allowed to fire up again. This 'anti-cycling' period is a normal function designed to protect the heat exchanger and improve energy efficiency.
You may notice this status more frequently in spring and autumn when your home requires less intense heat to reach the desired temperature.
DIY fix possible
Wait 5 to 10 minutes for the status code to change automaticallyCheck that your room thermostat is set to the desired temperatureEnsure radiators are turned on to allow heat to dissipate
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Vaillant models that show the S.08 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax
- 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.08 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