Extrusion problems prevention

Updated 3 months ago ​by Martin Lexa

Before you embark on the wonderful journey of 3D printing, there are several things you should know to avoid getting stranded right after you've set the sails. Carefully reading this article will endow you with the knowledge of how to prevent your 3D printer's extruder getting jammed. If, however, your filament already refuses to come out from the nozzle, or if you hear the extruder motor skipping steps, seek the information of how to clean the hotend in this article.

As usual, the first thing to check is the firmware version, always use the latest one! Double check that you have flashed the correct firmware for your printer version!


Always use the latest Prusa Slicer version and enable automatic updating of built-in presets under Configuration -> Preferences.
Live Z too close to the bed

Make sure you have performed the First Layer Calibration. Avoid compensating lack of adhesion by squishing the first layer too much. If the nozzle is too close to the build plate, it can clog as the filament does not have enough space to spread out. Adjust the Live Z value every time you move the printer to a different location, when you print with a different type of filament or when you swap the steel sheet from the textured one to the smooth one and vice versa.

Slicing profile and settings

Be careful what settings you are choosing when preparing your g-codes, as they also store information about materials (and thus temperatures), not just about extruder movement. For example, printing ABS with PLA temperatures will clog the nozzle almost instantly. The same applies if you are experimenting with nozzles with different diameters, never print a gcode sliced for 0.4 nozzle if you have 0.25 one installed.

The correct temperatures may vary based on the manufacturer and are always stated on the box and on the spool. If need be, you can increase the hotend temperature during the print in LCD menu -> Tune -> Nozzle by 5 °C.
Incorrect loading/unloading

When loading a new filament, preheat the nozzle to the temperature required by the previous filament type you have used as it's remnants are most likely still in the hotend. For example, if you have printed with ABS or PETG and want to print with PLA now, load the PLA filament at the ABS or PETG temperature. This way, the newly introduced filament can push the old one out.

Afterward, make sure to set the temperature to PLA, don't let it bake in the hotend too long!


Loose hobbed pulley

Inspect the hobbed pulley (Bondtech gear) on the E-motor shaft, see if it is tightened by the small grub screw against the flat part and if it's not slipping. Moreover, check if the gear is aligned with the filament movement following the manual (MK2/S here).

Secondary Bondtech gear

Make sure the secondary Bondtech gear located in the idler door can rotate freely. Check if the shaft didn't slip and if it is not sticking out too much only to one side. If the gear does not turn, take it out very carefully and inspect both tiny bearings that are supposed to be inserted in the gear.

The driving extruder gears require regular maintenance, for more information, see this article.
Hotend Assembly

While it has to be tight (hot-tightened) to prevent the filament from leaking out, there is supposed to be a space (around 0.5 mm) between the nozzle head and the heater block. Also, there must be no gap between the nozzle and the heatbreak, these parts have to be touching each other inside of the heater block.

Besides that, verify if the heatbreak that connects the heater block and the heatsink is not crooked or loose.

If you need to change one of the components of your hotend, refer to this guide (for MK3S/MK2.5S/MMU2S. For MK3/MK2.5, there is a separate guide).


Extruder fan

Clogs are sometimes caused by the hotend having the incorrect temperature for the given filament. One of the root causes of this issue can be a malfunctioning extruder fan.

  • First, check it visually and observe if and how it spins. Make sure it is clean of any filament strands and dust.
  • To be 100% sure that both fans are OK, you can go through the Selftest which can be found in LCD Menu -> Calibration -> Selftest.
  • Make sure that the hotend fan is attached to the extruder properly. While spinning, it must push air inside, not outside.

Idler tension

Too little or too much tension on the extruder idler spring can also cause issues with filament extrusion. With the idler screw being too loose, the gears can't grip the filament and the motor can start skipping. With the idler screw being too tight, the teeth on the gears might grind the filament and get choked.

The head of the idler screw should be aligned with the Extruder Body (see the photos above). In case of the MK2/S, the tension springs are on the outside of the extruder. The length of the compressed tension springs should be 13 mm.

Dirty extruder gears

Both of the aforementioned extruder hobbed pulleys (Bondtech gears) have teeth that bite into the filament in order to move it. Make sure your extruder gear(s) are clear of any leftover plastic. You can clean the pulley teeth with a small brush (the harder the better).


Filament preparation

Before inserting a filament into the extruder, make sure there is no bulk on its end. Ideally, Cut the tip of the filament at a 45-degree angle using the bundled pliers. In general, make sure the filament thread you are inserting is as little bent or deformed as possible.

Try another filament

Cheap, low-quality filaments are the most common cause of uneven extrusion, skipped layers or even clogged nozzles. Many manufacturers perform only spot checks on the diameter of the filament, which makes them miss bulges or changes in the filament shape. Our Prusament, on the other hand, has a guaranteed ±0.02 mm diameter precision and the ovality is checked multiple times per second by a laser sensor.

Baked filament

We do not recommend leaving your hotend preheated for a long period of time while the filament is loaded. The filament can disintegrate inside the nozzle or heatbreak and turn into a black goo. That is why the firmware of our printers contains a safety timer that shuts the heating of the hotend off after 30 minutes. Still, you don't want to reach 30 minutes too often.

Wet filament

Moisture from the air can easily ruin your 3D printer filament. This doesn't concern only Nylon, Poly-carbonate and water-soluble filaments, but also, for example, PLA and ABS. If you see any bubbles coming from the nozzle, hear any hissing, popping or cracking and the extrusion is inconsistent, the filament needs to be dried. Always store your filaments in a dry area or ideally in a dry box.

Printing TPU/Flex

Before you start printing from a flexible, elastic filament such as Flexfill, clean the nozzle from the previous material with a cold pull. When loading it, loosen the extruder idler screw(s) a bit and leave them loosened during the entire print. Flexible filament likes to jam in the hotend during retractions, so lower their number as much as possible and slow the overall printing speed down.

Printing composite materials

Printing materials such as Woodfill, (and other wooden filaments) or Bronzefill (plus other metal filaments) can be also quite difficult and "cloggy". Make sure to clean the nozzle from the previous material with a cold pull before you start. Using a wider nozzle (0.5 mm and more) is strongly recommended.


Find out more troubleshooting tips here: Community Forum | Assembly Manuals | Youtube channel | info@prusa3d.com

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