No heating ... but real big battery use with 2 phone calls one day while I have also had a persistent problem with the Fingerprint ID getting lost and not functioning.
Apple has a restore iOS protocol.
http://www.apple.com/support/iphone/assistant/restore/
My iMac USB issues and the GBs of third party software I use really makes it impossible for me to do a restore the way Apple recommends
So I made an appointment with the Apple Store Genius and asked them to put the iOS 8.4 into the iPhone and set it up as new.
The Genius Tech pushed down the 'Home' and 'On' button until the Apple USB logo came on as that procedure makes the Firmware available for update ... and then plugged the iPhone into the USB cord (only one was used) attached to a MacBook Pro 13 inch with trackpad and keyboard integrated into the computer.
Nothing else was on the USB line except for the iPhone, and only the Apple OS was on the MacBook with the iTunes working the restore to factory settings ... and lucky them, they had the iOS software there on the hard drive.
No internet connection what so ever ... only took 5 minutes and I was out the door.
Now the Fingerprint ID problem is gone .. but calling AAA emergency road service and a auto repair shop recently cost me 47% of battery life.
I did not know it took so much energy to make 2 phone calls and was shocked to make the discovery.
Anyhow .. ME doing the iOS restore at home ... did not work what so ever.
Problem persisted as it was software corruption apparently ... that I was the maker of given my own circumstances.
So that is my fix that is working fairly well for me is to have the Genius do the iOS restore ....
oh ... be sure your contacts are backup under the 'Info' setting in iTunes ... as doing the necessary re-install of the music, apps and contacts after making the factory settings restore at the Apple Store is then so much easier.
Only thing left to do after that is work the Apps for the first time ... as a new install ... and put in the information required to make them work such as my AAA membership number ... etc.
Also with the new iTunes on my iMac, it defaults to iCloud for backup when it sees the new iPhone, and for me to make backup to my computer (iMac) I have to click that specific button and then click 'Apply' for it to stay working that way, as it seems the iPhone is the one who remembers that my computer is the back up; but iTunes has to tell it so.