Cold pull problem, Thermistor maybe?  

Cold pull problem, Thermistor maybe?

I've posted here before about extrusion problems I've been having with my Mini.  I've tried a number of things, I've replaced the hot end PTFE, I've replaced the nozzle, I've replaced both at the same time following these instructions https://help.prusa3d.com/en/guide/how-to-replace-a-hotend-ptfe-tube-mini_119449

I've had mixed success, it seems after replacing something it prints well for a time, but then begins to screw up.   The PTFE tubing I used during the replacement was tubing I had in stock and cut based on the jigs available from Prusa https://www.prusaprinters.org/prints/3644-ptfe-tube-chamfer-and-cut-jig

Recently I made a purchase from Prusa and ordered some of the pre-cut tubing.  While I was waiting for the shipment my extruder started acting up again so as soon as I got the new tubing I replaced it.  It made things much, much worse. 

I've never done a cold pull with my Mini so I decided to try it.  I heated the nozzle to 253, hand pushed Prusa PLA Azure Blue through the nozzle, set the temp to 90, and pushed until I couldn't push anymore.  When it hit 90 I gave it a tug, it wouldn't budge, so I tugged harder and the filament snapped leaving a little bit in the nozzle.  I tried again with the same result.

I'm now wondering, could my thermistor be at fault?  The problems I'm experiencing could be caused by my hot end being too cold.  Is it likely that my thermistor is reading a higher temperature than it's really experiencing?

It seems unlikely to me that using a genuine Prusa PTFE tube, a genuine Prusa nozzle and genuine Prusa filament that I'd still be having problems.

Thoughts?

Thanks

-Bob