Install a different launcher (
Nova Launcher has never been reported to heat the phone up, and I've never had it happen after a few years of running it) and see if the phone still overheats. If it does, the phone is still under warranty, and whatever is causing the overheating would be covered. If it stops overheating, it's the launcher causing it, so you'll have to use a different launcher. (Action Launcher doesn't cause my Note 3 to overheat - I just installed it to try it - but it could act differently on different phones.)