So my Roku was working rock-solid for over a year without any issues. One evening it started popping up "Your device is overheating" warnings ever minute. It had never given me even one warning prior and we're now into the fall season so if anything it's colder. Here's how to fix it.
Get one of those phone-fixing kits with various picks to pry the plastic off the front of the device. Try to make sure your body is grounded and free of static-generating clothing (polyester shirts/sweaters should be avoided.) Take the board out of the enclosure. You'll see an aluminum case, you'll need to pry the lid off. You may need a magnifying glass or lamp to carefully pry the lid off. Be extremely careful, there are microscopic surface-mount components close to the lid! Do everything you can to avoid touching any of them, but also don't mutilate the lid taking it off, it needs to fit back tightly after.
Once the lid is off you'll see dried up heatsink compound on the processor. This is the cause of your overheating. I had some fresh non-conductive compound from a different heatsink I got for my CPU, but you can buy it by itself, it's not expensive. Clean off the dried up compound and apply a good amount of fresh one. Close the lid and make sure it makes good contact with the compound and the processor. Test the unit to make sure it's working and not overheating then place back in its case. You're done. Overheating problem solved.
