measured temperature extruder too high

my mendel is finally ready to go, however the thermistor measures a temperature of about 800c as soon as i hit the "switch heater on" button. I guess this is also the reason why the wire doesn't start heating.

I have double checked if the wires are connected correctly and there is no short-circuit. I have uploaded the latest firmware for gen6 that works with the g550 thermistor, so the thermistor settings should also be ok.

any suggestions?

Measure the resistence of the thermistor at room temperature.
ASS-U-ME that it is a 100k thermistor you should be reading around that...

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

I had the same issue - the leads crossed at one point, they are not insulated. This is a NTC resistor, so the resistance gets lower with higher temperature.
[en.wikipedia.org]
[en.wikipedia.org].
Maybe the leads touch right at the beginning.