Your S5 should not run "hot" but warm would be normal as when charging or heavy use of the phone or some apps. I feel you may have some apps and programs running that you are not aware of. Go into settings when the phone is hot and check your app usage and see what apps are running at the time. You can then shut down and may even be able to uninstall some app that is a problem for you. However be very careful has to what you do shut down. Certain apps are needed for normal operation of your phone. If not sure ask questions on the forum. Their will be someone to help you.