BoilerFaultCodesVaillant S.33 Fault Code
Also written as S33 — same fault.
The Vaillant S.33 fault code means: your boiler is currently running its internal fan to clear air or gases before it attempts to light, but it is waiting for a signal to confirm it is safe to start.. It appears on 13 Vaillant models in our database.
Technical description: Forced fan operation until the pressure monitor is switched
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the S.33 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 825 Repair: £150-300
- ecoFIT Pure 830 Repair: £150-300
- ecoFIT Pure 835 Repair: £150-300
- Home Combi 25
- Home Combi 30
- Home Combi 35
- Turbomax 824/828 Repair: £150-350
- Turbomax Plus Repair: £120-300
- Turbomax Plus 824/828E Repair: £150-350
- Turbomax Plus 828 Repair: £100-280
- Turbomax Plus 828 E Repair: £150-350
- Turbomax Plus VUW 242E Repair: £150-350
- Turbomax Plus VUW 242EH Repair: £150-350
Source
Vaillant S.33 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 835 manual (PDF)
- Vaillant Home Combi 35 manual (PDF)
- Vaillant Turbomax 824/828 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026