Some warmth is normal when your phone is being charged or when it is being used extensively.
However, if the heat is significant or when it doesn't cool down once you close down apps - you might want to contact customer support.
Hope this helps, have a lovely day!
It happened to me the first time I charged it, and only on the first time. It was not boiling hot but it was hot. Since that, it charges from any previous charge level to 100% fast and almost cold. During the time I have it only felt it little warm once or twice when charging and using the phone.
It's pretty much cold charging now. Again charged it today from 42% to 100% in less than 2 hours and it was cold charging with a protective cover.