Stuck extruder after fillament runout and change  

Mike Daneman
Estimable Member

I was trying to maximize my filament usage and printed some simple parts using a roll that was nearly out and, when it ran-out and the printer paused due to filament sensor, I feed a new roll of filament into it.  When the filament sensor triggered, I pushed the knob to unload filament, which, of course, didn't unload because there was nothign left to unload.  I then fed the new filament and it extruded some through the nozzle and went back to printing.  This is the first time I did this and initiallay thought it worked, but then I walked away from the printer shortly after the filament change and came back to see that the extruder jammed and it completed the print "printing in the air".  I got the extruder unjammed, but was wondering if I did somethign wrong in how I fed the new filament.

The filament that ran out had a bend at the end where it was attached to roll and I wonder if that's what made it jam.  Do you guys have experience with filament running out and how to best deal with it?  Should I generally avoid letting this happen in the future or should I make sure the last bent piece of filament is cut off?  Any advice?


Posted : 23/10/2019 11:58 pm
Honorable Member

Make sure the bent piece is cut off or it will not feed as you found. When the sensor triggers for end of filament it should unload itself ready for you to remove it.

Posted : 24/10/2019 12:30 am
Illustrious Member

When the sensor triggers, there should be filament in the gears (the sensor is well above the gears).  Usually, the filament is "bent" at the end where it attaches to the spool; this bend gets caught in the sensor area and won't unload, and a disassembly of the sensor ball is required.  Sometimes removing the cover is enough, and with dexterous use of tweezers you can fish out the bad end; otherwise, you can open the idler door, cut the filament at the gear, pull the upper fragment down and out, and heat the extruder and pull the lower fragment up and out (pliers help that last pull).

It is always wise to get more than one opinion...
Posted : 24/10/2019 5:06 am
Active Member


I've noticed the same thing happening after the 'bent' end disappears beneath the sensor cover and jams when the 'unloading' process starts as you stated. 

Do you (or anyone) know of a method or 'trick' to resolve this?

Waiting till the end of a spool of filament just to catch the end from going in reminders me of the high maintenance and attention my MK2 requires. One of the reasons I purchased an MK3S was for the filament sensor but if I have to remove a jam each time it is a bit frustrating. 

Any thoughts, comments, or suggestions would be appreciated. Thank you. 


Posted : 02/01/2020 3:31 am
Active Member

I'm almost in the same boat. Managed to get it out without cutting it in half so I didn't get an extruder jam. But then those noises appeared. Do some of you have them?

Is there an easy way to clean the ball housing without disassembling everything?

This post was modified 1 year ago by bgoner
Posted : 03/01/2020 12:50 pm
Active Member

We should definitely ask Prusa to include this in the manual, no matter how much they don't want it: "If the end of the filament is bent the filament fail system won't be able to push the end of the filament back and it will jam. If you are close to the end of the spool cut the bent end if you want the feature to work." 

Or something similar.

They definitely know about this. Maybe they don't want to mention it cause its admitting that the feature does not work as advertised.

p.s. - fixed my squeaky noise with compressed air in the filament hole by holding the filament sensor lever open as much as possible.

This post was modified 1 year ago by bgoner
Posted : 04/01/2020 8:14 pm
New Member

The manual has a procedure that work when your problem happened to me. I had to take some extra steps, but this is a good place to start:

None of the filament is going through the nozzle
If none of the filament is going through, then most likely, your hotend got clogged. In order to fully clear it, please follow these instructions:

1. Heat up the nozzle to 250 °C for PLA or 270°C for ABS jams.

2. Wait 3-5 minutes and then go to LCD Menu - Load filament. If you cleared the clog and the filament went through, simply lower the temperature to normal and re-do load filament again.

3. If the filament loads successfully, you can resume printing.


In addition to the above, I pulled the end of the filament (visible when opening the idler door) out very "carefully". A heat gun, dutifully aimed, may have helped, but I went the he-man route (brute force).

Posted : 17/09/2020 7:43 pm

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