Hello . The first thing you will need to check if the thermistor is good, is the heater relay on the PCB board. It should have a blue and black wire going to it. Test there and see if you have 240 volts with the unit turned on. If not, you will need to replace the PCB board. The HE code is for a heater error. If there is 240 volts at the relay, you will need to test ant the heater and trace and see where your loosing voltage at. Hope this helps.
Part number: AP4244205 