Bad nozzle temperatures (-10 deg c)

[Tropicalsq744]

Hi,

I recently replaced my thermistor after accidentally dislodging it. It worked fine (temp roughly the same as bed), PID autotune also worked too (changed the values slightly).

After autotune, the temps started showing def for both nozzle and bed, and after restarting the printer a few times the temps came back. But this time the nozzle is a good 40 deg lower than the bed (reading -10 currently).

So my question is, did the thermistor just give up on me? (While fixing it up, the glass on one side was a little chipped. Didn't have any spare so I thought i'll just use it first) or was it a autotune problem?

Many thanks!

[Earthbound]

When LCD shows "def" for temperature, it usually means there a bad connection in the thermistor wiring. Poor connection also tends to make temps read low. A cold solder joint is a likely culprit.

[DLS3141]

I would say your thermistor is damaged to the point that it now has some intermittent failure. Since it's a critical part of the system that keeps your hotend temp under control, I'd err on the side of caution and replace it.

I damaged my thermistor the first time I had to disassemble my hot end. I was frustrated enough to figure out how to make one that threaded into the hot end instead. I also replaced the resistors with a cartridge heater and eliminated all of that messy permatex from my hotend. I recommend it. You can buy threaded thermistor assemblies...if you don't want to buy one, I can show you how I built mine.