User error and faulty programming
I came to my mk 3 the other day and the bed was saying it was at 50c trying to reach 60c. In touching the bed it was clearly far hotter than that even the bed carriage was very hot.
It turns out the thermistor had been dragged out of its tape and was dangling by the connector. My assumption is it's lead was hanging out the bottom of the control box and caught on the bed going back and dragged the cable out.
My question is surely the firmware should have triggered a thermal runaway error if the bed couldn't get to temperature after a reasonable time.
Re: User error and faulty programming
It seems like it should hit thermal runaway. I've never seen thermal runaway on my mk3, but on the latest Marlin builds on my Ultimaker I saw it (annoyingly) when the PID was slightly out of tune and my nozzle couldn't maintain 240 but stuck at 232 during heavy extrude. I lost several prints that way before I tweaked the PID and the thermal runaway margins.
I never saw it on the bed, however, only on the hot end. Do you know for certain that Marlin/Prusa firmware has be thermal runaway detection? Seems like it should, but I can't confirm it.
It's also possible that 50c was within the runaway margin of 60c so it didn't trigger.
Re: User error and faulty programming
My highly modified Anet A8 with the E3d V6 Bowden goes into thermal runaway error sometimes when you change the extruder temperature which is very frustrating.