BoilerFaultCodesVaillant S.02 Fault Code
Also written as S02 — same fault.
The Vaillant S.02 fault code means: your boiler is simply completing a brief self-check and starting the pump before it begins heating your radiators.. It appears on 19 Vaillant models in our database.
Technical description: Heating mode: Pump pre-run. The pump prerun for heating mode is activated.
What causes the Vaillant S.02 fault?
This status occurs when the boiler receives a signal to provide heat and begins circulating water through the system before ignition. It is a normal safety and efficiency feature designed to clear any residual heat and ensure the pump is functioning correctly before the burner fires. Your boiler has not broken down; it is simply preparing the internal components for the heating cycle.
This code is most frequently seen in autumn and winter when the central heating is first being used regularly after the summer break.
DIY fix possible
No action is required; this is a normal operational status message.Wait approximately 20 to 60 seconds for the code to change as the boiler fires up.Ensure your thermostat is turned up if the boiler remains in this stage for a long period.
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Vaillant models that show the S.02 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
- ecoTEC pro
- ecoTEC sustain
- Home Combi 25
- Home Combi 30
- Home Combi 35
- 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.02 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 435 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026