Unresolved 3D printer turns off completely

Replacement of the thermistor will require some :
1) care, it is small and fragile
2) attention to detail (the leads must be covered with the insulation to prevent them shorting) and the therrmistor needs to be positioned correctly on the hotend heater block
3) soldering since the wires will need to be re-soldered when you replace the old with the new Make sure to use heat shrink over those connections as well since you do not want the thermistor to ground out.

If you look at the original wiring you can get the gist of how it needs to go back together. It is not super complicated. Practice soldering other wires first if you need to.

 

That looks like an r1+ hexagon. Is there a set screw under the thermistor ?

Edit: and does it look like a brass colored sleeve in the hole ?

 

Yes its an r1+ hexagon. You have to get ahold of robo for a replacement thermistor. They are the only ones im aware of that have those.

The other option is to swap to a serviceable hotend or replace the whole hotend

 

You can use another Hexagon, you can use the prometheus or the E3D

If you do get the hexagon I would suggest getting it from Robo3D directly as theirs is a bit different. The others you can get pretty much where ever you like. A caution on the E3D "clones" -- you get what you pay for so stick with the real deal if you want that one.

 

Pretty much an 1.75mm hotend will work with the machine. Even a J-Head style if you wanted to go that route (but, why?)