BoilerFaultCodesVaillant F.72 Fault Code
Also written as F72 — same fault.
The Vaillant F.72 fault code means: your boiler has detected that the two pipes measuring temperature are giving very different readings, which usually means a sensor is failing or there is a blockage in the system.. It appears on 29 Vaillant models in our database.
Technical description: Fault: Flow/return sensor - Temperature difference between flow and return temperature sensor is too great
What causes the Vaillant F.72 fault?
This fault occurs when the boiler's internal computer notices that the flow and return pipes have wildly different temperatures, which shouldn't happen during normal operation. The most common reason is that one of the temperature sensors has become faulty or uncalibrated, though it can also be caused by a physical blockage or a pump failure preventing water from circulating correctly.
This fault often surfaces when the heating is first turned on after summer, as internal components like the pump can seize or debris can settle during long periods of inactivity.
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.
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A cover plan would handle faults like F.72: no call-out fees, no surprise bills.
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Vaillant models that show the F.72 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 412 Repair: £150-250
- ecoFIT Pure 418 Repair: £150-250
- ecoFIT Pure 425 Repair: £150-250
- ecoFIT Pure 435 Repair: £120-250
- ecoFIT pure 612 Repair: £150-£300
- ecoFIT pure 615 Repair: £150-£300
- ecoFIT pure 618 Repair: £150-£300
- ecoFIT pure 630 Repair: £150-£300
- ecoFIT Pure 825 Repair: £150-250
- ecoFIT Pure 830 Repair: £150-250
- ecoFIT Pure 835 Repair: £150-250
- ecoFIT sustain 415 Repair: £120-£220
- ecoFIT sustain 418 Repair: £120-£220
- ecoFIT sustain 430 Repair: £120-£220
- ecoFIT sustain 615 Repair: £150-£300
- ecoFIT sustain 618 Repair: £150-£300
- ecoFIT sustain 630 Repair: £150-£300
- ecoFIT sustain 825 Repair: £120-220
- ecoFIT sustain 830 Repair: £120-220
- ecoFIT sustain 835 Repair: £120-220
- ecoTEC exclusive Repair: £120-£220
- ecoTEC plus Repair: £90-160
- ecoTEC plus VU GB 656/4-5 A Repair: £150-300
- ecoTEC pro Repair: £120-£220
- ecoTEC sustain Repair: £120-220
- Home Combi 25 Repair: £150-£300
- Home Combi 30 Repair: £150-£300
- Home Combi 35 Repair: £150-£300
- Home Regular 12
Source
Vaillant F.72 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 435 manual (PDF)
- Vaillant ecoFIT pure 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026