Velleman dualhead K8400 isolator peek smelt

Good day best 3d printer builders and users.

I was very proud when my first 3d printer, which I had bought as a building package, immediately reacted when the powerplug was put in the wall.
Less happy was I, when I saw that after giving a print job the peek insulator started to melt.
The temperature feedback must there because I saw the temperature on the display. (is this conclusion correct?)

Is this temperature display in accordance with the temperature that is present in the heatherhead??

IE what makes my dual head so hot that the peek insulator starts to melt?

                       best regards and thanx in advance,  Pietjebel....

Sounds like the thermistor is not in the correct position.