BoilerFaultCodesVaillant d.35 Fault Code
Also written as D35 — same fault.
The Vaillant d.35 fault code means: your boiler is struggling to switch between heating your radiators and heating your hot water supply, which means you may experience issues with one or both of these services.. It appears on 29 Vaillant models in our database.
Technical description: Diverter valve position (ecoMAX 800)
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.
- Atmomax Repair: £0-120
- ecoFIT Pure 435 Repair: £180-350
- 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 Condensing 600/800 series Repair: £180-350
- ecoMAX System 612 Repair: £180-350
- ecoTEC Plus 615 Repair: £150-250
- ecoTEC Plus 620 Repair: £150-250
- ecoTEC Plus 625 Repair: £150-250
- ecoTEC Plus 635 Repair: £150-250
- ecoTEC Plus 840 Repair: £150-250
- ecoTEC plus aquaPLUS
- ecoTEC sustain Repair: £150-250
- Home Combi Repair: £150-300
- Home System
- Thermocompact Repair: £150-250
- 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 System 612 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026