Bed/hot end heaters worked for a day, then died a mysterious death  

Bed/hot end heaters worked for a day, then died a mysterious death

Hey folks!

I got my Mk3 kit last week and built it on Saturday. I was able to run two prints with no problems. The next morning (Sunday), I started a third print, watched it print successfully for 15 minutes, then when I came back to it, it had stopped the print with a thermal runaway error.

I cleared the bed and ran the sefltest, and got a heater/thermister not connected error (before axis check, so I think it's the bed?). I turned off/unplugged the printer and checked the board. I unplugged and replugged the hot end heater and thermister, unplugged and replugged the bed thermister, and checked that the heated bed connections were solid. I then flipped the machine and made sure the bed thermister was in place, then followed all the appropriate wires from the bed and thermister to make sure there were no pinch points or damage.

I re-ran the self test an hour or two later, and it passed the heated bed and failed the extruder. When I try and preheat both of them, their temps initially rose a little bit before halting. Trying to preheat again a few hours after that, didn't move at all.

Monday morning, I turned on the machine and asked it to preheat. The hot end heated as expected, but stopped when it got to ~120, then the element turned off and it started cooling. The bed warmed very slowly, up to ~30, then turned off and started slowly cooling. I didn't get any errors, and the target temps stayed the same on the screen. Monday afternoon I tried it, and the temps didn't move at all, and the bed heating LED stayed off the whole time.

I think I'm gonna pull out all the wiring and re-check everything this evening. Is there anything else I can do? I'm worried because both heaters are failing sporadically.