I bought a complete MK8 replacement extruder set that comes with 100k thermistors, but they dont work on my mightyboard. it starts to read them and then goes ;lkajsefoiwa’rlkja’oivhha;lknve

Should i be able to change the thermistor from the existing to the new ones in the firmware? any suggestions?

The ctc uses a type k thermocouple not a thermistor. Re use ones of your original block.

That’s correct regarding the thermocouple. Not only must it be the correct thermocouple it must be electrically isolated from the heater block. Most sold on eBay are not. You must source a reliable thermocouple specifically for 3dp. Electric noise will cause errant readings, and a heater short to the block will send 24 volts to the thermocouple amplifier, which is fatal. If your in the U.S.I recommend either flashforge or uncle Chuck. http://www.unclechucks3dprinterstuff.com

As has been said, the MightyBoard does not use Thermistors; it uses Thermocouples. (And it’s not an either/or situation like some boards.)

If it’s been less than a year since you got your printer, contact your eBay seller. Most of the listings say the printer comes with a 1 year warranty. I had a thermocouple go out on one of my extruders, and the seller sent me another for the cost of shipping because it was still under warranty.

i ordered new thermocouples

I know this is an old topic and likely has been resolved but for the sake of anyone else that finds this as useful info, I am running on both my CTC and my Replicator 2 these thermocouples Amazon.com with a non insulated ring terminal http://amzn.to/2gwIQpP crimped on. I have been running these for a combonation between the 2 printers for around 500hrs now.

As adamcooks says you will indeed get interference if care is not taken, it is not only annoying when it gives incorrect readings that screw up prints, it could be damaging to your board, as a work around I simply wrap the thermocouple, or the ring terminal tip in some kapton tape http://amzn.to/2hJtUWH

I also clipped my original thermocoulple wires up above the extruder a ways an installed these plugs Amazon.com this makes changing out thermocouples and servicing the extruder easy, no need to unhook at the board. I also used RC style deans plugs on my heater cartridges, and fans http://amzn.to/2httPaq same deal make it easy to take apart for maintenance.