BoilerFaultCodesVaillant D.75 Fault Code
Also written as D75 — same fault.
The Vaillant D.75 fault code means: your boiler has timed out because it has been trying to heat your hot water cylinder for too long without reaching the required temperature.. It appears on 11 Vaillant models in our database.
Technical description: Maximum charging time for a storage without own controller
What causes the Vaillant D.75 fault?
This fault occurs when the boiler detects that it has been running for an unusually long time without successfully heating your hot water cylinder to the set temperature. The most common reasons are a faulty sensor failing to report the correct temperature or a mechanical part, like a valve, getting stuck and preventing hot water from reaching the cylinder.
This issue is often more noticeable in winter when the incoming cold water mains temperature is lower, forcing the boiler to work longer to heat the cylinder.
DIY fix possible
Check that the valves on your hot water cylinder are fully openEnsure your thermostat or programmer is calling for hot water correctlyTry resetting the boiler to see if the fault clears
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →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
- Combi Compact 242EB Repair: £100-280
- Combi Compact 282EB Repair: £150-350
- ecoFIT pure Repair: £100-250
- ecoFIT Pure 412 Repair: £150-350
- ecoFIT Pure 418 Repair: £120-450
- ecoFIT Pure 425 Repair: £100-250
- ecoFIT Pure 435 Repair: £120-350
- ecoFIT Pure 835 Repair: £100-350
- ecoTEC Repair: £100-250
- ecoTEC plus Regular Repair: £100-280
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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026