This fault according to Vaillant Instructions and Servicing manual is a Flow and/or return NTC fault, whereby the temperature difference between the Flow and Return NTC sensors are too high.
Cause of F72
Specifically Flow and/or Return NTC is defective, caused by tolerances too big. In simple terms, the reading being reported are not in line with manufacturers expected readings.
Models applicable to:
Ecotec Pro, Ecotec Plus, Ecotec Exclusive.
Before simply replacing the NTC sensors or jumping to conclusions.
- Things to check:
- Make sure the resistance of the Flow NTC is 12K ohms at 20C (degrees celcius).
- Make sure the resistance of the Return NTC is also 12K ohms at 20C (degrees celcius).
- You should check the connections from the NTC all the way back to the PCB. Removing and re-inserting carefully. Using a multimeter, you can test the wiring harness to make sure there is no break or partial break in the cable.
- Check the X20 Connector of which the NTC harness is connected to.
- That the NTC sensors are on the correct pipe. Usually blue wire is the Heating Return NTC and the red wire is the Heating Flow NTC
NTC Flow / Return Sensor