BoilerFaultCodesVaillant D.35 Fault Code
Also written as D35 — same fault.
The Vaillant D.35 fault code means: your boiler is currently switching over between its heating and hot water functions.. It appears on 36 Vaillant models in our database.
Technical description: Not relevant
What causes the Vaillant D.35 fault?
This status occurs when the internal diverter valve physically moves to switch the flow of heated water between your radiators and your hot water taps. It is a normal mechanical process where the boiler pauses momentarily to ensure heat is directed to the right place. You will see this on the screen briefly during transitions, such as right after you turn off a hot tap while the heating is on.
DIY fix possible
No action is required as this is a normal status message rather than a fault.Wait a few moments for the boiler to complete its cycle.If the boiler appears stuck, try a simple reset by pressing the flame button.
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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 418 Repair: £180-350
- ecoFIT Pure 425 Repair: £150-250
- 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 824E Repair: £180-300
- ecoMAX 828E Repair: £150-300
- Ecomax Condensing 600/800 series Repair: £180-350
- ecoMAX System 612 Repair: £180-350
- ecoTEC
- ecoTEC Plus 615 Repair: £150-250
- ecoTEC Plus 620 Repair: £150-250
- ecoTEC Plus 625 Repair: £150-250
- ecoTEC Plus 630 Repair: £150-250
- ecoTEC Plus 635 Repair: £150-250
- ecoTEC Plus 840 Repair: £150-250
- ecoTEC plus aquaPLUS
- ecoTEC Pro / ecoTEC Plus Repair: £150-300
- 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 manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026