I had the same problem, it was because it is summer and I am in the garage at around 100 degrees F. I fixed it by pointing a floor fan into the printer and the prints finish now.
The thermal break tube did you replace it when you changed the nozzle? some times incorrect installation wear on the PTFE lining or using one that doesn’t have a thermal break in the threads has ptfe tube through the whole throat of the tube, or no ptfe in the tube at all will cause symptoms like you are describing.
I am using this one it has a partial ptfe lining and the thermal break in the threads, it has a tapered inside diameter on the filament inlet side too.
Mine has started this as well. 3 years old now so I am going to replace the heater extruder block assembly to see if that does it as I have done all the other simple and cheap replacements. So now I am going to try the $300 dollar one and just replace the main block.
Did a replacement on the stepper motor, stepper chip, nozzle, fan, and extruder drive wheel so now time for the big change up.
This usually happens when the nozzle gets hot and somehow dissipates the heat into extrusion mechanism. Make sure feeder teeth doesn’t get hot, otherwise it skips. Turn off the fan and try to print very slowly with lowest temp (like 180C for PLA at 10mm/s), give it a try and see what happens. If it happens after like an hour later then that’s it. You need better isolation.
I have the same problems on my Replicator 2X. The reason can be many things:
bad leveling
extruder gear needs to be cleaned
hot end temperature to low or to high
filament quality → amount of non-plastic particles in the filament or just dust on the filament tend to burn off and that lead to a clogging nozzle or at least giving the extruder a hard time to push the filament through the nozzle until the point it’s to hard and the extruder gear is milling into the filament.
friction of filament in the PTFE tube. Some filaments have higher friction than others. It’s also material dependend. Some PLA doesn’t move very well through the tube. ABS instead slips easily. Maybe you give it a try without the tube.
Retraction. Yes, retraction! For some reasons the chances of getting a clogged nozzle raise when using retraction. I’ve disabled retraction for some filaments and was able to print successfully
The spring for the pushing ball bearing in the extruder is too weak. I’ve replaced it with a stronger one in the left extruder of my Replicator 2X. Granted, I haven’t tested that extruder yet, but I have another printer with a Mk8 china extruder pushing its teeth as deep into the filament as the my left extruder now does and with the Mk8 I didn’t had that issue for 2 years now. And that printer is running 80% of 24/7.
Have you updated the software . If so take the nozzle off and hit it with a blow torch to make sure it’s clean or buy new tips . If that doesn’t work . Take it apart and clear the clog . The thermo barrier or nozzle . Or just buy the new extruder . It’s 129 I think supposed to be better don’t know .