Extuder temperature spikes in GUI

[joesomething]

Hello,

As shown in the photo, my extruder temperature immediately jumps when it approaches 240-degree, then returns. Anyone seen this before? It doesn't affect my prints, but it does cause some oscillation in the overall temperature. Here's some info:

-PID calibrated
-tried 2 heaters
-tried 2 thermocouples
-does not seem to happen at 180, 200 degrees

Thanks

[rrdavis]

Maybe a bad thermocouple.

[fwiffo]

Yes, this is usually a false-contact, I experienced something like this (and I had to change thermocouple, because there was a false contact almost at the end), I would suggest to check the wiring and even check if the thermocouple is correctly wired and the wire itself didn't broke.

For the sake of you I must suggest that you don't use the toolhead, because a false-contact might cause an incorrect revealed value, thus making the toolhead itself go over the input temperature. You can imagine the consequences. (usually the firmware would reveal something like this, but if the contact is not open for a long amount of time, it can get unnoticed)