How do you unblock a nozzle  

RE: How do you unblock a nozzle

Hi DJ

Here is an image that I am going to discuss

Normally the screwthread at the end of the nozzle assembly, is screwed into the heater block below the heatbreak and  from the top of the heatbreak upwards would be inserted inside the  Nextruder Heatsink. 
In use the Filament would be pushed into the tube of the nozzle, where it would pass through the heat break into the melt zone, and out of the Nozzle.
during printing the filament will be continually pushed into the melt zone,  and out of the nozzle. when there is a retraction, the hot filament is drawn into the heatbreak and cooled.  safely (this is why you should not to large retractions with a Prusa direct drive  extruder(One cause of Heat Creep))

What I believe happened when the nozzle securing screws came loose, the nozzle  dropped and messed up your model, in the process the shaft of the nozzle above the heatbreak would have been exposed, allowing it to heat  up, this would have been OK whilst filament was being pushed through the nozzle,  
When you discovered the problem and restored the nozzle to it's normal position,  the hot filament in the accidental melt zone will be cooled by the heatsink, and become solid... causing a blockage   the extruder will not be able to move this filament, 
What you will have to do, is raise the extruder to say 40mm above the build plate set the nozzle to heat to say 280C (the modern printers that have Nextruders, Mk3.9. Mk4 and XL)  loosen the  nozzle retaining screws, lower the nozzle and allow the extended area to heat, Support the heat break with a screwdriver or pair of wire cutters so that you are not stretching the cables, and use the Move Axis (E Axis) option, to move filament through the nozzle, as the filament is moving, begin to slowly raise the nozzle  back towards it's normal position, the aim is to begin moving cold filament into the extended melt zone, as you slowly reduce the size of the extended melt zone. It looks like the Move Axis menu option only moves 200mm of filament at a time, so press the LCD Switch twice to reset the value to '0' and continue. 
Eventually you should have the filament extruding normally, with the Nozzle back in it's normal location, when this happens, re tighten the nozzle retaining screws, and dispose of the waste filament. and your extruder should work properly. Make a note for yourself to check the tightness of the screws periodically.    

regards Joan

RE: How do you unblock a nozzle

Joan,  I've had filament get stuck in at about the same location (about 20 mm up the tube) when printing CF-PETG. One roll in particular. In none of my cases were the thumbscrews loose. 

I wish I had thought of your method to clear the blockage.  My method involved using a small torch to melt the plug and driving the filament out the nozzle with a metal rod.  Unfortunately that rod has to be removed while still hot and it drags filament with it which deposits onto the inside of the heat break and prevents filament from moving freely down the tube.  I had some long 1.8 mm drill bits to clean that out, but your method, while just as tedious, seems much better. 

I gave up printing with that filament and haven't had ant recurrence. 

RE: How do you unblock a nozzle

cheers Lynn, 
3D printing is a complex balance of conflicting issues... 
Not all issues have the same cause. but sometimes one solution can address different issues... 

Welcome to the confusing world of Polymers
with earlier printers I would remove the nozzle to make heatbreak clearing more simple.    that is not possible on the Nextruder nozzle. 

I did consider wire... but I couldn't think of where to get a suitable probe, where I cam currently staying, 
Hence the alternative approach. 

Joan