Boiler displays F72, inconsistent readings between flow and return sensors

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Incorrect NTC type fitted, One of the NTC sensors faulty, Wiring swapped between flow and return sensors, PCB sensor input fault

Safety: Isolate power and allow the boiler to cool.

Steps:

Check that both flow and return NTC sensors are genuine Protherm parts and of the same type.
Verify that the wiring from each sensor goes to the correct PCB connector; correct any cross‑wiring.
Measure resistance of both sensors at the same temperature and compare; replace any sensor that is out of tolerance.
If sensors and wiring are correct, the PCB may be faulty and require replacement.

Medium 3/5

Flow NTC Sensor

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