One year ago I installed my streaming stick on an older HD tv using the Roku extender cable and powered using the Roku AC adapter. I never received an overheating device message on the tv screen despite sometimes 3 hrs. of Roku use. A few weeks ago I replaced the tv with a new 4K UHD model and installed the streaming stick the same way. I've been watching HD programs with the stick without problems, again sometimes for several hours. The other night, for the first time, I began watching a 4K UHD streaming movie on one of the Roku channels and after about 15 minutes was surprised to see the overheating device message on the TV screen. I checked and the stick was hanging freely with no cables or other items touching the case or very close by.
I learned by doing a little web research that the stick uses more power processing a 4K UHD signal than a HD signal and therefore it was reasonable that it should run hotter. I suddenly realized that the weight of the antenna bar on the power cable that attaches to the stick via a mini USB cable combined with the flexibility of the extender's cable was causing the stick to hang almost vertically. All the heat being generated inside the stick's case was dissipating vertically, up though other already hot components rather than straight out through the case. After unplugging the power cable and allowing the stick to cool, I re-positioned the power cable so that the antenna bar was supported rather than dangling freely. When I plugged the mini USB power cable back into the stick, this time the stick was almost completely horizontal (as it would be if I connected it directly to a HDMI port on the side of the tv). This AM I watched the same 4K UHD movie for a full hour that previously had caused the overheat message to come on the screen after about 15 minutes. The overheat message didn't appear. I haven't had time to watch any 4K UHD content for longer than 1 hour, but so far, so good. Bottom line (tentatively): Don't let the stick hang vertically when using the extender and watching 4K UHD programming on a Roku channel.