BoilerFaultCodesVaillant d.75 Fault Code
Also written as D75 — same fault.
The Vaillant d.75 fault code means: your boiler has taken longer than it should to heat up your hot water cylinder, which usually means the heat isn't being transferred efficiently from the boiler to the tank.. It appears on 18 Vaillant models in our database.
Technical description: Maximum cylinder reheating time
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.75 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £120-250
- ecoFIT Pure 418 Repair: £120-450
- ecoFIT Pure 425 Repair: £100-250
- ecoFIT Pure 435 Repair: £120-350
- ecoFIT Pure 825 Repair: £150-350
- ecoFIT Pure 830 Repair: £150-250
- ecoFIT Pure 835 Repair: £100-350
- ecoTEC 65kW Repair: £150-300
- ecoTEC sustain Repair: £150-300
- Home Combi Repair: £120-250
- Thermocompact Repair: £100-200
- Turbomax 824/828 Repair: £120-250
- Turbomax Plus Repair: £120-250
- Turbomax Plus 824/828E
- Turbomax Plus 828 Repair: £120-250
- Turbomax Plus 828 E Repair: £120-250
- Turbomax Plus VUW 242E Repair: £120-220
- Turbomax Plus VUW 242EH Repair: £120-250
Source
Vaillant d.75 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 65kW manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026