Quote Originally Posted by printbus View Post
One possibility is that the thermistor becomes partially detached and starts reading low. That's definitely a possibility if the thermistor is just taped onto the hot end. I had good luck with the muffler sealer being used as glue. That's an improvement over the tape. Tapping the aluminum block for use with a stud-mount thermistor is even better (gmay3 has done this; I'm using a different aluminum block on my hex hot end that was already tapped).
The E3D hotend I use has a screw to hold the thermistor in its hole. I like it much better than wrapping the head in Kapton tape to keep it in.