Thermistor issues after update  

Thermistor issues after update

I have a MK3, been great for years, zero issue. I updated the firmware to the latest and tried to print something and it failed, Thermal Error, something like that, the alarm for it is insane btw. So I assumed that after all these years the thermistor had failed, I did the selftes thing and it stopped on the Heater/Thermistor not connected. So I replaced the thermistor. Before I bundled up the wires I did a self test and all was ok, passed every test. Bundled up the wires nice and neat like in the assembly instructions. Turn it on, self test fails. same message Heater/Thermistor not connected...

wires are all checked, took everything very carefully out and out it all back, read some post somewhere about a firmware issue and thermistors, but flashing back to previous firmware didn't do anything either. same message no matter what I do. I did the calibration thing for the hotend and it fails and said thermal error, once it said thermal runaway (but it hadn't even started to heat)

of course this was the first time anyone asked me to print them something, I was like sure, I can print anything...I was printing just fine till three days ago...

any help out there for the old MK3?