Just got back from the Apple store. The phone heated up again while using WAZE and charging in the car. Outside temp. was 83F. Phone screen dimmed so dark that I was unable to see anything tried to close the app. but the screen touch was unresponsive. The screen remained dark for about 10 minutes...lucky I was at Apple and they were able to see how dark it had become. They ran diagnostics on the phone and did see that the heat sensor had triggered. They had no explanation for what was happening. They seem to feel that the phone is operating normally... I've never had any other iPhone perform like that. Bottom line, they are ordering a one time warranty replacement under my apple care. If it continues to happen they will try a software reload.