Extruder issue

SO my extruder stopped heating up. It would not read tempature nor heat up so i changed the heater and the thermistor. I am not sure if i used the correct thermistor but I used a ntc 100k

so now when i power it on the extruder temp reads 400 degrees and will not change and the extruder still dos not heat up. ive checked all my connections 1000 times, anyone have any ideas? im sure its something simple that im missing

Thanks in advance

Sounds like your thermistor is shorted to ground some where. Or both leads are shorted together. A high temp reading means the control board is seeing a very small thermistor value. The closer to ground you get the hotter it thinks the heater is.

could it be that the control board itself is bad and thats causing the issue? as not quite sure where it would be shorted out i tried 3 different extruders on it and none of them work also tried 2 separate dual extruders on it and only one side of the dual extruders will heat up.

what normally caused the issue was a failed print. when i returned to check on the print all the plastic had stuck to the extruder and melted completely around it. this is when the problem first happened and would no longer heat up or read any temperature from that point is when i changed the heater and the thermistor which is where im stuck now with the extruder reading 400 degrees but not heating

I believe I have cancelled out the control board being an issue as I put the same extruder on a working printer and it read 400 on that one as well, so must be an issue with the thermistor or extruder itself. However this still does not explain why two different brand new dual extruders will only heat up on one side? Any help with why the thermistor is reading 400 ad will not change nor heat up as described in original post or wht the dual extruders are only heating on one side?