'HE' error causes
*Could be Low or High AC Voltage (below 108V or over 132V)
*Could be loose/dirty heater element connections..check element leads at circuit board
*Element bad.....check resistance of element (58-68 ohms)
*If element tests OK.....could be circuit board
You state only get when plugged into outlet at home.....15/20A?
What 'other' devices are on that same circuit?
Error clears when you run generator...or plug into a real RV receptacle (50A) or have you tried that AFTER you get the error?
Cause if OK on gen/50A after error on house outlet.........then house outlet/AC power would be suspect vs fridge.