My dishwasher (same model number) is also throwing the HE code.
I started by taking it out and checking the thermistor and it was bad so I ordered one from here:http://www.repairclinic.com/PartDetail/Control-Board/ADZ32992801/1367007?modelNumber=LDF7932ST
I didn't check to make sure the new one was good but assumed it was. Of course, it threw the HE code right away on the first wash after the replacement so I'm kicking myself for not checking the heating element in that part.
The hot water is 122 degrees so I'm guessing it's not the mainboard. Furthermore, the mainboard was replaced under warranty about 18 months after getting the dishwasher so I'm hoping I have the new one anyway.
The repair manual says "to confirm steam generator error, press "delay start and rinse only" buttons simultaneously. However, it doesn't say to do this while the HE error is flashing or after. I'm hoping that will narrow it down but right now with the HE error flashing, pressing the buttons isn't doing anything. Also, there is no "rinse only" just a "rinse button so I'm assuming it's the rinse and delay start buttons simultaneously.
So, I turned it off and back on again, just tried to push those two buttons without the HE error flashing and still I don't get anything.
I also can run it through the steam cycle so I'm thinking that maybe the heater in the bottom of the tub could be the bad one.