Printer keeps jamming when printing Prusament PLA  

Active Member

I've had a variety of challenges printing over the last few months, but they've all really been centered around issues around jamming. It's such weird behavior. The print will get a few hours in, then start jamming. The filament sensor doesn't even detect it, just notice it because the extruder starts skipping steps.

I've tried:

  • Cold pull
  • Replace nozzle
  • Replace drive gears
  • Reprint fan shroud (got a bit melty when I had a thermal runaway last year)

What's odd about it is, I'll usually cancel the print and let my printer cool down. After it has cooled down, I can start printing again like the jam magically cleared itself. So it doesn't seem to be physically jammed, just partially jammed? I have no idea.

For the most part, my printer is a stock Mk3s (upgraded from Mk3). Over the past year, I've replaced the hot end fan, heaterblock/nozzle/thermistor/heater cartridge.

I'm not sure if it's related, but I'm also seeing underextrusion, so I'm not sure if that is caused by a partial clog or what. 

I'm slicing with the latest PrusaSlicer for Prusament and have the 3.9.3 firmware on printer. 

At this point, I'm out of ideas. I can't really trust my printer to print anything at this point and don't know what else to try. Any ideas would be greatly appreciated!

Posted : 21/03/2021 9:10 pm
Active Member

I should also mention I'm wondering if this might be cooling related because on at least a few occasions, the support material has been pretty well fused onto the print which I haven't had happen before. Maybe the part cooling fan is dying?

Posted : 21/03/2021 11:20 pm
Honorable Member

Have you cleaned the fans?

Clean both sides of the blades with a stiff paintbrush and use tweezers to pick out any strings/hairs clogging the hub.


Posted : 22/03/2021 4:06 am
Active Member


I just did. The hotend fan was still perfectly clean, also replaced in November/December along with my thermistor. The part cooling fan had a good amount of dust on it, but I cleaned that off. 

I have another print going now, we'll see how that goes. 

Posted : 23/03/2021 2:14 am
Antonio da Catania

I don't have the MK3/S but I have read somewhere that this kind of issue can occur due to the extruder motor getting hot, the PLA will get soft too soon and cause the jam.

I saw people solving attaching some heatsinks or fans to the extruder motor

Parlo italiano...but I'm not an expert....
Posted : 23/03/2021 8:58 am
Active Member

So my print last night (one of the presliced PLA gcodes here printed completely fine. Which was puzzling to me as I would have been shocked if a light coating of dust would cause the jamming issues.

So I thought some more about it and decide to try a retraction test. Specifically this one which is pre-sliced: and within the first 10-15 minutes it started jamming and the print looks pretty bad. 

And @antonio-da-catania, I had also seen people talk about. I've been occasionally touching my extruder motor just to get an idea of how hot it gets. Occasionally I'd consider it "warm", but never hot. I think I've heard of people describing themselves almost getting burned by their extruder motor. When it was jamming during that retraction test, I'd say it was barely warmer than ambient temp (ambient = ~21.5c)

Posted : 23/03/2021 3:37 pm
Active Member

I ended up disassembling and reassembling the extruder and swapping in a new heatbreak. It's printing a lot better now. Maybe I didn't have something fully tightened before

Posted : 31/03/2021 6:24 am

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