Extruder thermistor issues

Sounds like the input on the controller is shorted. Not much you can do but replace the controller. Since you used a known good thermistor that rules out it. Have you ohmed out the wires from the thermistor to the board? That would be the only other thing.

Just so you can understand how to read issues on a thermistor problem here is crash course in thermistor 101 in case you don't know how they work.

Essentially a thermistor is a resistor. But unlike normal resistors that have a fixed value, e thermistor has a variable value that changes depending on the external temp around it or the surface it is in contact with.

At low temps the resistance is high and at high temps the resistance goes low. For the particular thermistors we normally use the resistance at room temp (around 23c) should be close to 100Kohms.  If you look at the graph below it will give you an idea of what the resistance of a functioning thermistor is like at given temps.

So try to measure your distance again. You did not say if that 258 was at room temp or heated.

I connected the bed temperature sensor to the extruder temperature input and It is doing the same thing as before so the problem isnt related to the thermistor. How do I test with the input pins on the board to see if they are definetely the problem. Also if I reupload the firmware to the board could that potentially fix the problem. I had a look at the board and could not see any issues.