A few iPhone 7 models built with Intel chips were reported to overheat and completely stop working. Especially when reactivating the phone. It also applies to the A1660 model built with Qualcomm chips. Unfortunately, I had one of these lemons and the main cause of failure, the phone stopped working on cellular. The cellular radio works fine but a “switch” chip on the board prevented them from turning on. I tried a new SIM and firmware reinstall but all gave me the same message at setup, “unable to activate, phone needs update.” There is a video on YouTube about how to repair it but my guess is the phone was recently repaired unknown to me, bought on eBay, and I would say the replacement chip is not large enough to accomodate the overheating I felt before the phone failed and the nearby components are out of spec—I’m not willing to fix it. Here is Apple’s acknowledgement of the problem: https://support.apple.com/iphone-7-no-service