Extruder and bed over temp error/problem

I am having an issue with my SD2. I had a thermistor (extruder) blow and now with a replacement I get a huge over temp, on both the ext and bed. Both are showing at 270+deg constantly.

The extruder did not run over 195 at any stage.

Here is what I have tried:
- tested connections on both
- changed both thermistors
- disconnected both thermistors (no change in temp)
- connected thermistors to the board (no change)
- reinstalled firmware and tried all the above again.

I am out of ideas here and have not seen any posts that are even close to this issue. I would love some help!!

Cheers