BoilerFaultCodesVaillant d.71 Fault Code
Also written as D71 — same fault.
The Vaillant d.71 fault code means: your boiler has reached its maximum allowed internal temperature limit for the heating system to protect the pipework and components.. It appears on 27 Vaillant models in our database.
Technical description: Max. target value for heating-system flow temperature
What causes the Vaillant d.71 fault?
This fault occurs when the water leaving the boiler exceeds the maximum temperature limit set in the internal software. It is usually caused by a lack of water circulation, often because radiator valves are closed or the pump is struggling to move heat away from the heat exchanger quickly enough.
This issue often appears during the first cold spell of autumn when heating is turned back on after months of disuse, potentially revealing a seized pump or stuck radiator valves.
DIY fix possible
Check that at least two or three radiators are turned fully open (valves turned anti-clockwise).Ensure your magnetic system filter is clean and not blocked.Restart the boiler to clear the advisory status.
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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 Condensing 600/800 series Repair: £150-300
- ecoMAX System 612 Repair: £120-250
- ecoTEC 65kW Repair: £150-350
- ecoTEC plus 637
- ecoTEC plus aquaPLUS
- 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 425 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant Ecomax Condensing 600/800 series manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026