Radds Help

I am new to radds and need some help.
I an trying to fit it to a Delta. I had it fitted and axis moving, I intended to fit a Diamond hot end later so wanted the extra extruder ability.
I heated up the standard Mk8 hot ends and printed a test cube. Modified the firmware and started a second print. three layers in the printer stopped. The hot end was reporting a temperature of 635C it had instantly risen from 190C. By the time i looked it was too cool to extrude so it never overheated.
I changed the thermistor but this one reads the same. i changed the thermistor to the next input and it reads the same on this input. if i put it on the HB input it reads the correct room temperature.
What has broken??? the rads board or the Due.
I have emailed Ozznest who i brought both from but got no response.
Please help

There's a short somewhere or the Arduino Due has a problem.

So I should replace the Due as i have looked for shorts and couldn't find one?
What could have caused this as i don't want to repeat it again.
Thanks for the fast response.

You did use a multi-meter to make sure the thermister is reading correctly at the connector on the wire? If everything looks fine, it wouldn't hurt to try another Due.

Unless a voltage greater than 3.3vdc was put into the Due pin, it should be fine. That could occur if the power supplying the hotend heater was shorted to the thermister.

Again thanks I have ordered another Due.
I checked the thermistor with a multi tester and the thermistor works on the old Geeetech board.
The heaters are new as I want to use 24Volts so replaced them.
I think i better check if they are shorting out when heated prior to fitting the new Due.