BoilerFaultCodesVaillant d.35 Fault Code
Also written as D35 — same fault.
The Vaillant d.35 fault code means: your boiler is struggling to tell the difference between heating your home and heating your tap water, which may cause your radiators to get hot when you only want a shower.. It appears on 23 Vaillant models in our database.
Technical description: Diverter valve position 1 = hot water; 0 = heating system
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.35 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 825 Repair: £150-250
- ecoFIT Pure 830 Repair: £180-350
- ecoFIT Pure 835 Repair: £180-350
- ecoMAX Repair: £180-350
- ecoMAX 613 Repair: £180-300
- ecoMAX 618 Repair: £180-350
- ecoMAX 622 Repair: £180-350
- ecoMAX 635 Repair: £180-350
- ecoMAX 824/2 E Repair: £180-300
- ecoMAX 828/2 E Repair: £180-300
- ecoMAX 835 E Repair: £180-300
- Ecomax Condensing 600/800 series Repair: £180-350
- ecoTEC sustain Repair: £150-250
- Home Combi 25 Repair: £150-300
- Home Combi 30 Repair: £150-300
- Home Combi 35 Repair: £150-300
- Turbomax 824/828 Repair: £180-300
- Turbomax Plus Repair: £180-300
- Turbomax Plus 824/828E Repair: £180-350
- Turbomax Plus 828 Repair: £180-300
- Turbomax Plus 828 E Repair: £150-£250
- Turbomax Plus VUW 242E Repair: £150-300
- Turbomax Plus VUW 242EH Repair: £150-300
Source
Vaillant d.35 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 Ecomax Condensing 600/800 series manual (PDF)
- Vaillant ecoMAX 835 E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026