Hi all, We assembled our printer, hooked it up, and tested the motors. Then we tested the hot end... We clicked preheat, and once it reached 80 degrees C, we clicked 'off'. We noticed smoke coming from the hot end, so we looked back at the software to find the temperature had climbed to 500 C+ [preheat temperature was supposed to be 230 C]. We clicked 'off' multiple times to no avail, so we unplugged the printer, but the casing for the hot end had already melted and the heating element was glowing red hot. Does anyone have thoughts on why this may have occurred? We ordered another Jhead, but want to be sure this doesn't happen again.