BoilerFaultCodesVaillant S.00 Fault Code
Also written as S00 — same fault.
The Vaillant S.00 fault code means: your boiler is currently idle because it has not received a signal from your thermostat or timer to turn the heating on.. It appears on 9 Vaillant models in our database.
Technical description: Heating: No heat demand. The burner is off.
What causes the Vaillant S.00 fault?
This code appears when the boiler is working perfectly but is simply waiting for a command to start. It means the internal computer has not received an electrical 'call for heat' from your wall thermostat or plug-in timer. The most common reasons are that the temperature on your thermostat is set too low, the timer is in an 'off' period, or the batteries in your controller have run out.
This is frequently seen during the transition into autumn when homeowners forget to turn their thermostats up or replace batteries after the summer break.
DIY fix possible
Check that your room thermostat is turned up higher than the current room temperatureEnsure your heating programmer or timer is set to 'Auto' or 'ON'Check that the batteries in your wireless thermostat are not dead
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Vaillant models that show the S.00 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant S.00 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant Turbomax 824/828 manual (PDF)
- Vaillant Turbomax Plus manual (PDF)
- Vaillant Turbomax Plus VUW 242EH manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026