BoilerFaultCodesVaillant D.71 Fault Code
Also written as D71 — same fault.
The Vaillant D.71 fault code means: your boiler is currently set to run at its maximum possible heating temperature, meaning it is working as hard as it can to heat your radiators.. It appears on 30 Vaillant models in our database.
Technical description: Maximum setting of heater control knob
What causes the Vaillant D.71 fault?
This code appears when the heating temperature dial or digital control has been turned up to its highest possible setting. It occurs because the boiler is being instructed to deliver its maximum heat output to the radiators, often after someone has manually adjusted the controls for more warmth. It is a status indicator rather than a broken part.
This is more common during extreme cold snaps in winter when homeowners turn their thermostat or boiler dial to the maximum setting to combat the freezing weather.
DIY fix possible
Locate the heating control knob on the front of the boiler panel (marked with a radiator icon).Turn the knob slightly to the left to reduce the target temperature to a more efficient level (e.g., 65-70°C).Observe the display to ensure the temperature setting has updated.
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Vaillant models that show the D.71 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax
- ecoFIT Pure 418
- ecoFIT Pure 425 Repair: £0-60
- ecoFIT Pure 435 Repair: £0-120
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835 Repair: £0-120
- ecoMAX Repair: £0-120
- ecoMAX 613 Repair: £120-250
- ecoMAX 618 Repair: £120-250
- ecoMAX 622 Repair: £120-250
- ecoMAX 635 Repair: £120-250
- ecoMAX 824E Repair: £120-250
- ecoMAX 828E Repair: £120-250
- Ecomax Condensing 600/800 series Repair: £150-300
- ecoMAX System 612 Repair: £120-250
- ecoTEC
- ecoTEC 65kW Repair: £150-350
- ecoTEC plus aquaPLUS
- ecoTEC Pro / ecoTEC Plus
- ecoTEC sustain
- Home Combi
- Thermocompact
- Turbomax 824/828
- Turbomax Plus Repair: £120-250
- Turbomax Plus 824/828E
- Turbomax Plus 828
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant D.71 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