BoilerFaultCodesVaillant F.71 Fault Code
Also written as F71 — same fault.
The Vaillant F.71 fault code means: your boiler has detected that a temperature sensor is sending a stuck or frozen reading, preventing it from heating your home or water safely.. It appears on 52 Vaillant models in our database.
Technical description: Fault:Flowsensor Flowtemperaturesensorsignallingconstantvalue: – Flowtemperaturesensorincorrectlypositionedatflowpipe – Flowtemperaturesensordefective
What causes the Vaillant F.71 fault?
This fault occurs when the boiler's internal computer notices that the flow temperature sensor is sending exactly the same temperature reading for too long, even while the burner is firing. The most common reason is that the sensor has physically failed or developed a high resistance, meaning it can no longer detect the actual rise in heat. It can also be caused by a loose connection or damaged wiring preventing the sensor from communicating correctly with the main control board.
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 F.71 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £90-160
- ecoFIT Pure 412 Repair: £150-250
- ecoFIT Pure 418 Repair: £150-250
- ecoFIT Pure 425 Repair: £150-250
- ecoFIT Pure 435 Repair: £150-250
- ecoFIT pure 612
- ecoFIT pure 615
- ecoFIT pure 618
- ecoFIT pure 630
- ecoFIT Pure 825 Repair: £120-220
- ecoFIT Pure 830 Repair: £150-250
- ecoFIT Pure 835 Repair: £150-250
- ecoFIT sustain 415
- ecoFIT sustain 418
- ecoFIT sustain 430
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoFIT sustain 825
- ecoFIT sustain 830
- ecoFIT sustain 835
- ecoTEC Repair: £90-160
- ecoTEC 65kW Repair: £150-250
- ecoTEC exclusive Repair: £95-170
- ecoTEC exclusive 627
- ecoTEC plus 412 Repair: £150-250
- ecoTEC plus 415 Repair: £150-250
- ecoTEC plus 418 Repair: £150-250
- ecoTEC plus 424 Repair: £150-250
- ecoTEC plus 430 Repair: £150-250
- ecoTEC Plus 610 Repair: £150-250
- ecoTEC plus 612
- ecoTEC Plus 615 Repair: £90-160
- ecoTEC plus 618
- ecoTEC Plus 620 Repair: £90-160
- ecoTEC plus 624
- ecoTEC Plus 625 Repair: £90-160
- ecoTEC Plus 630 Repair: £90-160
- ecoTEC Plus 635 Repair: £90-160
- ecoTEC plus 637 Repair: £90-160
- ecoTEC Plus 826 Repair: £150-250
- ecoTEC Plus 832 Repair: £90-160
- ecoTEC Plus 840 Repair: £90-160
- ecoTEC Plus 938 Repair: £90-160
- ecoTEC Pro Repair: £100-220
- ecoTEC Pro / ecoTEC Plus Repair: £90-160
- ecoTEC Pro 24 Repair: £100-220
- ecoTEC Pro 28 Repair: £100-220
- ecoTEC Pro 30 Repair: £150-250
- ecoTEC sustain Repair: £90-160
- Home Combi Repair: £150-250
- Home System Repair: £90-180
Source
Vaillant F.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 ecoFIT pure 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026