That's correct - it heats to -1 -2 -3 below, then (forever) it goes down one, up one, vacillates, but never gets up to the heating temperature. Doesn't go to next function. No trick helps, if I set it to less, it simply does the same relative thing.

I'll try reloading the firmware, I'm not skilled enough to put a pot in place of the sensor. BTW, this particular machine (not mine) has two extruders and one is broken. (I am sure I'm reading the good one) Would replacing the extruder be the fix, and where's a good place to get a new one? This is a GeeeTech PI3 Pro C.