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 36 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.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →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
- Combi Compact 242EB Repair: £90-160
- Combi Compact 282EB Repair: £90-160
- ecoFIT pure Repair: £150-250
- 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 825 Repair: £120-220
- ecoFIT Pure 830 Repair: £150-250
- ecoFIT Pure 835 Repair: £150-250
- ecoMAX Repair: £100-£180
- ecoTEC Repair: £90-160
- ecoTEC exclusive Repair: £95-170
- ecoTEC plus Repair: £90-160
- ecoTEC Plus 610 Repair: £150-250
- ecoTEC Plus 615 Repair: £90-160
- ecoTEC Plus 620 Repair: £90-160
- ecoTEC Plus 625 Repair: £90-160
- ecoTEC Plus 630 Repair: £90-160
- ecoTEC Plus 635 Repair: £90-160
- ecoTEC Plus 65 Repair: £90-160
- ecoTEC Plus 826 Repair: £150-250
- ecoTEC Plus 832 Repair: £90-160
- ecoTEC Plus 836 Repair: £90-160
- ecoTEC Plus 840 Repair: £90-160
- ecoTEC Plus 938 Repair: £90-160
- ecoTEC plus Regular Repair: £150-250
- ecoTEC plus System Repair: £150-250
- 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 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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026