Preheat error  

Preheat error

I have a Prusa i3 Mk2 assembled by Prusa. The printer worked ok for a couple days. In the middle of a print I got a THERMAL RUNAWAY error.

After resetting, now I get PREHEAT ERROR.

I checked the Thermistor by applying some heat to the nozzle and temperature increased, so I believe it is ok.

I checked the Rambo mini board, all fuses are good, when I turn on preheat, the contacts on the board show 12 volts, so I believe the board is ok.

I then checked the hot end cartridge.

I connected my ohm meter from one of the hot end cable to the partially exposed wires next to the hot end cartridge. BOTH wires on the hot end cartridge show that they are connected to BOTH wires on the cable, which makes me think something is shorted or the cartridge is bad.

The wires on the hot end cartridge are bent back at an extreme 90 angle, causing some of the wire insulation to be exposed. It is hard for me to tell, but i believe the exposed wires of the hot end cartridge could have been touching the outside edge of the hot end cartridge. Could this cause a short?

Also one strand of the wire at the hot end cartridge appears to be severed. Is this just one of several strands of wire?

Any ideas of what I can do?

Should I replace the hot end cartridge?

Do I need a specific one or just any that are 12 volt?

Please advise.