Dryer stopped heating but was otherwise functioning normally (drum turning, light on, control panel functioning). I checked the power at the circuit breaker box and at the plug and everything was normal. At that point I began googling.
I first put the dryer into "installation mode" per LG's website recommendation. This told me I was blocked by 80% (a "d80" on the display). I examined the tube in the dryer, my flexible line inside, and my exhaust vent that goes outside and all were clear. When I looked outside, though, I saw that the flap over the vent had been clogged with lint that had gotten wet from rain and solidified enough to hold the flap mostly closed. I cleaned that off with soap and water and tried the installation tests again. This part of the story ends here because I never could get that test to show anything other than ”d80.” I know that test will always fail on subsequent runs when the drum heats up because you're supposed to start with a cold dryer, but my dryer wasn't heating up. During the rest of this, I cleaned everything thoroughly and never found any lint build up or blockage I would've thought could have been a problem.
Anyway, the web and sites like this suggested the next most likely culprit was the high limit thermostat. I ordered one and used the video to go through the process. The video quality was excellent. I did realize that it wasnt going to be perfect because my dryer had a steam function that really changed up the layout of the wiring. My advice is to watch the video and name or number the steps, and get a little cup for all the screws and use your name/numbering system. Second, take pictures! I especially recommend picturesof any wiring harnesses you unplug.
What ended up happening is that I couldn't remove everything from the "top" of the dryer like the video showed. It looked like a very complex process to clear that area because of the steam assembly and because a new or different circuit board is off to the side. But you can take the dryer drum out the front without dumping all the control panel stuff over the sides. I ended up tying up the steam assembly so it would stay elevated after I took off the metal bracket in the top front. It worked out.
When I got the old thermostat out I tested the resistance, which should have been zero or very low at room temperature (it's a switch, so it should've been open or "on" at room temperature). There was infinite resistance (meaning the switch was instead closed or "off"). I then checked the new thermostat I ordered. As expected, at room temperature the resistance was zero. I knew then that at least I was replacing a truly broken part.
Reassembled the dryer and it worked like a charm. And no d80 error!
Thanks!