The logic board is a weak spot on these. I have 9 right now, and only have 3 in use. 3 are brand new still in the box, and 3 others are in storage. I used to have 12 when I bought broken units and combined good parts to make functional units.
The 3 currently in use all get warm randomly. I have a stereo pair and a lone HomePod. None of them are connected to the Apple TV 4K and I don’t even use them every day. The top surface of the right one in the stereo pair is warm right now and so is the one in the dining room. Neither have been used recently, and neither are an active HomeKit hub. I’m sure in a few hours they will cool back down like they always do. For a company so concerned about the environment, they should try making stationary objects last more than a few years. Why is my HomePod heating up, it’s not rendering a video?