BoilerFaultCodesVaillant d.33 Fault Code
Also written as D33 — same fault.
The Vaillant d.33 fault code means: your boiler is struggling to confirm that the internal fan is spinning at the speed required to safely vent exhaust gases, causing the unit to stop working to protect you.. It appears on 17 Vaillant models in our database.
Technical description: Required value of the rotary speed of the fan r.p.m. (837/637 only)
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 d.33 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 418 Repair: £250-£450
- ecoFIT Pure 425 Repair: £250-£450
- ecoFIT Pure 825 Repair: £180-350
- ecoFIT Pure 830 Repair: £180-350
- ecoFIT Pure 835 Repair: £250-450
- ecoTEC plus VU GB 656/4-5 A Repair: £250-450
- ecoTEC sustain
- Home Combi 25 Repair: £150-350
- Home Combi 30 Repair: £150-350
- Home Combi 35 Repair: £150-350
- Turbomax 824/828 Repair: £180-350
- Turbomax Plus Repair: £180-350
- Turbomax Plus 824/828E Repair: £180-350
- Turbomax Plus 828 Repair: £180-350
- Turbomax Plus 828 E Repair: £180-350
- Turbomax Plus VUW 242E Repair: £180-350
- Turbomax Plus VUW 242EH Repair: £180-350
Source
Vaillant d.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 425 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoTEC plus VU GB 656/4-5 A manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026