Force Needed to Push Filament into Hot End
I sometimes do a cold pull and remove the Bowden tube from the top of the hot end to push and pull the filament by hand. I recently had underextrusion, which was at least in part due to distortion of the PTFE tube in the heat break. I'm waiting for replacements. I noticed though that I can clearly tell by the force required to push the filament if the nozzle / heat break is clogged or not. I didn't have to put it all together to test it out. Of course, I might not have recognized the excessive force required if I had not done cold pulls before when things were correct and gotten a baseline for the required force.