Prusa i3 olmost on fire!

I guys,

Something really strange just happend,
I was busy changing/uploading my firmware, i started repetier, i did not give a command to heat up, and my e3d hot end kept heating up to 500 degrees celcius ( correct reading!!!)
Now everytime i plug in my power supply the hot end heats up, and keeps heating up, with no command given, ignoring the 250c max in the firmware!
What the hell is going on, all i changed was the steps per mm in the firmware.

I think if found the issue, i wanted to upload my modified firmware, but the communication.h ( repetier firmware) was missing, so i took the communication.h of my backup , afterwards i uploaded my modded firmware and this happend.
I now uploaded my backup firmware, with the same communication.h file , and all is fine now. very strange

Edited 2 time(s). Last edit at 12/19/2015 08:59PM by Govahnator.

I can however inform you guys, that an e3d v6 hotend that went up to 500 degrees, still works fine afterwards.

Edited 1 time(s). Last edit at 12/19/2015 02:30PM by Govahnator.

How long was it at 500C?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

You will need at least a new thermistor and maybe have to replace some bits of wire on the hotend end too if the insulation failed.
The thermistos won't survive temps over 350 for more than a few seconds until failing or at least producing totally wrong readings.
But if you could crank the temps up another 250 degree you could start to print in aluminium

It was at 500c for 1 minute atleast.

As far as i tested, the thermistor is fine,wich is strange i know.

I would replace the thermistor.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Mine went to 500+ for a bit, during a Marlin lock up. Replaced the ptfe, but not the thermister, and it's doing good now.