Troubleshooting Prusa i3 Mk3 extruder and hotend problems

Extruder and hotend problems are the most intimidating problems most users eventually encounter. They can be caused by a variety of problems, and fixes may only provide partial relief. My goal on these pages is to explain why problems occur and how you can resolve them.


Entire page needs to be reorganized and updated. Very rough at the moment.

The main thing to keep in mind is that the E3D V6 hotend is air cooled, and rated to work in ambient temperatures up to 40C. Exceed that for any one of a myriad of issues, and heat builds up to the point that low-temp filaments like PLA soften prematurely in the extruder, and you are likely to encounter skips and jams as the efficiency of the heatsink drops. A bunch of issues have been linked to these problems:

If the PLA softens, you can start to get into a feedback loop as increased friction contributes to extruder motor effort, contributes to heat… Turning up nozzle temps can help to a point, but also contributes yet-more heat to the picture.

By rectifying one or more of these contributing factors, it’s very likely you can get below the threshold at which problems occur. If you’ve got an enclosure, open it up for PLA. Improve airflow around the heatsink. Just keep this list in mind if you encounter the problem again as months get hotter. You may have to tweak several things.

In short: Anything that contributes to heat that can’t be vented away from the hotend (rated to 40C ambient) impedes air cooling efficiency. There are so many related factors that a problem with any one can cause a variety of feedbacks and problems. I’m willing to put money on the number of these posts declining rapidly once we’re out of the summer months.

A quick fix may be to switch over to printing with PETG if you can’t do anything about temps right away. Here’s a list of troubleshooting steps that I’ve put together after assisting and observing many Mk3 owners dealing with these problems on the Prusa forums and Reddit discussions.

Extruder and hotend problems tend to fall into three categories:

  1. Problems caused by heat

  2. Problems caused by hardware

  3. Problems caused by print settings

Understanding heat problems

Not surprising, heat is a big part of 3D printing using FFF technologies. Print too cold and you filament won’t feed. Print too hot and you’ll get stringing and other finish defects. Heat can contribute to a variety of other, far-less obvious problems, or be part of a combination or problems that can be difficult to pinpoint.

Under normal conditions, the “heatbreak” – a small gap between the cold heatsink and heated block – is sufficient to keep heat in the lower “hot” part of the hotend. Above the heatbreak, and large heatsink is intended to dissipate heat and keep it from moving up into the extruder area. This is the “cold zone” of the heatbreak assembly.

If heat creeps into the cold zone, either due to hot ambient temperatures, buildup of heat from the extruder motor, or from excessive retraction pulling molten filament to far up, problems can and will occur. Unfortunately, it can take time for heat to accumulate, so problems often don’t manifest until well into a long or complex print. Small diagnostic prints don’t generate enough heat to trigger problems, further complicating troubleshooting.


These notes are based on my experiences with the Prusa i3 Mk3 and Artillery/Evnovo Sidewinder X1 printers. If you are using a different printer, please verify the hardware details are similar.

To truly understand heat-related problems, you want to understand the limitations of the E3D V6 hotend used in the Prusa FFF printer line. This is an air-cooled assembly that is rated to operate at up to 40C ambient temps. If the ambient temperatures exceed this level, the cooling efficiency is increasingly diminished and can eventually lead to clicking, skips and jams.

Heat Symptoms

There are several common symptoms that can indicate heat-related problems:

  • Extruder clicks during printing.

  • Extruder skips or bucking during printing.

  • Filament jams and clogs.

  • Erratic under-extrusion.

  • Excessive extruder motor temperatures (too hot to touch).

Note that some of these can be caused by other factors besides just heat.


Heat-related problems doesn’t have any one cause. A 3D printer works best when a variety of mechanisms work in harmony. If one is off, print quality suffers and attempts made to fix one problem can quickly aggravate others.

  • Ambient temps matter. Particularly with the onset of summer, temps become a real issue. A room that is suddenly hot for you is hot for the printer as well.

  • Enclosures are designed to provide stable ambient temps. Prusa published a very popular blog post on constructing an inexpensive enclosure using Ikea Lack stands in April. After the initial burst of enthusiasm, many users ran into problems as spring temperatures turned into summer heat.

  • Cooling air path obstructions can be a real problem. Thingiverse is full of fun prints that put grills and other goodies on the printer. Unfortunately, some of these seriously impede airflow.

  • Excessive software retractions. This is really a software issue, but excessive retractions can contribute to heat as the extruder motor works overtime.

  • Over-zealous print speeds exceeding the maximum volumetric rate of E3D V6 hotend. If filament is pushed through faster than the hotend can process it, the result is back pressure up the filament path and ultimately to the extruder motor, causing it to work harder and thus generate more heat.

  • Motor current settings. Early firmware releases applied excessive current to the extruder motor, contributing to heat. Recent firmware updates (> 3.2.1) address altered motor currents.

PLA: The Canary of 3D printing temperature Problems

One indicator of heat-related problems is the inability to print PLA, which higher-temp materials such as PETG print without issue. This makes sense: PLA softens (has a glass transition temperature) much closer to the ambient temp many printers operate in. Add in some factors that add a bit more heat, and PLA can soften in the extruder. This can create feed jams and back pressure into the extruder.

Heat remediation

There are several things that can be done to reduce heat build-up in the extruder and around the hotend heat sink.

  • Improving airflow worked for some users. A simple table fan blowing around the hotend was sufficient to allow PLA printing during hot months.

  • Simply opening printer enclosures made the difference for many users.

  • Several users reported that early Mk3 kits shipped without the thermal paste between the heatbreak and heat sink recommended by E3D. Adding thermal paste improved cooling efficiency and reduced problems for many users.

  • Prusa released the R3 extruder parts intended to improve air cooling by opening up the extruder housing around the hotend heat sink. (Note that some users have complained of softening PINDA mounts and other problems with these parts.)

Mechanical problems

The Prusa Mk3 design is not fully optimized for some situations and this can cause problems. User modifications and mistakes can also cause problems.

  • A stuck or loose Bondtech extruder can cause feed problems leading to under extrusion, filament shredding and feed problems.

  • Build-up of filament fragments around the Bondtech gears in the extruder can lead to intermittent jams and feed problems.

  • The collet retraining the PTFE tubing in the heatsink can be missing or not locked properly, allowing the tubing to slide and cause problems.

  • Over- or under-tightened extruder gears can cause feed problems and filament shredding in the extruder.

  • A partial nozzle or hotend clog can be causes by a variety of issues.

  • The filament feed path from the top of the extruder housing into the Bondtech gears is not optimal in the current extruder design. It is offset by roughly 1mm, causing some feed problems.

  • Some owners get carried away printing the nice looking fan covers off Thingiverse and wind up killing airflow. The quiet Noctua cooling fan does not generate extra airflow, and a slick-looking cover can adversely affect is performance.

  • Filament dust filters have been installed incorrectly, jamming filament feed.

  • Complex filament feed paths can add friction and excessive feed tension, leading to under-extrusion and shredded filament.

  • At some point in 2018, Prusa began shipping a modified heatbreak with a wider throat at the top to rectify feed issues with the MMU2 issue. Unfortunately, this contributed to filament feed problems, particularly when coupled with excessive retractions (see below) and elevated ambient temperatures (see above). The non-Newtonian behavior of molten or soft filament no doubt contributes to this problem.

Remediating mechanical problems

Before trying more drastic measures, check the basic mechanical components of the filament feed path.

  • Inspect the Bondtech extruder gears and housing. With the right extruder cover open, inspect with a flashlight. Is the extruder area clear of debris? A rusty-looking smattering of dust is normal, but loose filament and other material is not. Blow it out, clear it with a brush if necessary.

  • Is the white PTFE tubing protruding from below the gears damaged? Replacement or reshaping of the PTFE tube may be required.

  • Inspect the extruder idler. Open the extruder right cover and verify. The idler on the right cover should spin freely without friction. If it can’t, feed problems and jams can occur. Verify the gear is properly inserted into the guides, and that the geared assembly spins freely.

  • Inspect the extruder tension screws. Is the filament visibly distorted or shredded? Too tight and the filament can be distorted and snag or jam, causing the extruder to do extra work and heat up. Too loose and filament doesn’t feed, causing the extruder gears to slip, resulting in clicks and jams. The screws normally protrude < 1mm from the left side extruder housing cover.

  • Check for partial nozzle blockage. Raise Z, heat the nozzle to print temp and extrude some filament. Inspect the filament as it is extruded. If the filament does not flow cleanly, or pulls to one side for more than a few seconds, do some cold pulls to remove any crud build-up in the nozzle and hot end.

  • Check for a clear filament feed path. Raise Z to max and open the extruder. Poke a 1.5mm rod down through the filament path, past the open Bondtech extruder gears and into the PTFE tube. If you remove the nozzle, it should poke through cleanly and without obstruction. See clearing filament jams for more details.

If these basic measures are inadequate, more drastic steps may be required:

  • Examine the PTFE tube for damage. Make sure there are no snags. Replacement may be required. Be sure the collet clip is applied properly to retain the PTFE tubing.

  • If you are not using a MMU2, consider replacing the Prusa stepped heatbreak with a standard E3D V6 heatbreak.

  • Investigate replacement extruder designs with corrected/improved filament feed paths.

Printing problems

Octoprint or other server software can cause problems if the hosting server (Raspberry Pi?) gets too busy. Try printing from SD card directly to see if the problem still occurs.

Do you experience failures with one material over others? Increasing temps slightly may improve flow. It might also contribute to unwanted heat.

Slicer settings


Needs work.

Retractions pull the filament up from the hotend to relieve nozzle pressure. This can help with oozing and stringing, but can also contribute to heat-related problems.

  • Are you using excessive retraction distances? The Prusa i3 Mk3 uses a direct feed mechanism. Many guides recommend retraction settings of 5mm or more which is appropriate for a Bowden setup, but not the direct feed mechanism of the Prusa i3 Mk3. If your retraction length is above 2mm, you are pulling melted material back up past the heat break. Keep retraction distances around 0.8mm.

  • Are you using overly-aggressive retraction settings? Does the point at which your print fails consist of lots of small areas (e.g. fingers) and retractions? Preview the sliced model in your slicer software to see if you have lots of retractions occurring in small areas. Increase the minimum travel required to trigger retractions as a possible troubleshooting step. Increase the minimum travel required to trigger retractions as a possible troubleshooting step. If using PrusaSlicer, Prusa sets the minimum move to 1mm. PrusaSlicer defaults to 2mm. Try 5mm. You may get some stringing, but can deal with that separately.

The E3D V6 hotend used on the Prusa i3 Mk3 can process roughly 11.5 mm3/s. Any attempts to move filament any faster through the hotend can result in back-pressure on the extruder or jams in the nozzle.

  • Does slowing the print down from the front panel (say to 50%) reduce problems?

  • Does adjusting slicer speed or volumetric feed settings reduce problems?

  • Over-zealous speeds exceeding maximum volumetric rate of E3D V6 hotend, causing skips & jams.

  • Prusa’s provided speed settings for most slicers are extremely aggressive. Their settings for PrusaSlicer set the flow rate for PLA to 15 mm3/s , which exceeds the E3D V6 capacity. Other materials are set to 1-10 mm3/s , which may explain why PLA fails and others work. Check your slicer preview for flow rates. Reduce max volumetric speeds if using PrusaSlicer. You may be stuck just reducing speeds with other slicers.

    • Increasing temps to increase flow.

Fan turned on to reduce stringing Hotend temperatures reduced Print temps increased

Avoiding problem prints

Reduce de-retraction speeds.

You can do some analysis to avoid many of these problems and judge the effectiveness of these measures yourself.

  • Slice your model in PrusaSlicer, save the gcode file.

  • Click on the Preview button at the bottom.

  • Select Volumetric flow rate in the drop-down box at left. Do you see it hitting or exceeding the 11.5 mm3/s mark at the places it commonly fails?

  • Select Feature types on the drop-down and enable showing Retractions with the checkbox. Do you see a lot of retractions at the failure points?

  • Select Speed in the drop-down and go through the layers until you hit the common failure point. Are speeds high at these points?

This analysis might help pinpoint why you’re having these problems short of replacing hardware (which may or may not fix the problem).


Move this to a separate page.

Dealing with Filament Blobs

Filament blobs can form inside the extruder mechanism when hot filament is pulled up into the extruder area and cools. These can sometimes be large enough to prevent removal of the filament through the top cover, requiring opening the extruder cover and snipping the filament.

One tip for avoiding blobs is to heat up the hotend and extrude a small amount (1 inch/25mm) of material before ejecting filament.

Ideally, you will be able to eliminate blobs from occurring using the steps listed above, but there are printable covers on Thingiverse that unscrew or swivel to allow removing the blobs without cutting.

Miscellaneous Notes

Others find the extruder idler sticking, creating more work. Others inadvertently use excessive retractions which contribute to the problem. Putting a comprehensive list of possible contributing factors would make for a very dull blog post! The R3 extruder parts were released to help with the problem, but obviously ambient temps and anything that adds heat is still going to work against you.

I think there needs to be a general “heat awareness” in the community. Prusa has posted info and there’s plenty about, but I see similar problems with other printer described in posts in the Reddit 3D printing forums as well. It’s one of those things that’s obvious once you’re aware of it, but that a new user might not immediately realize. Here’s a short list of heat-related problems:

We had a similar spate of “heat creep” and “extruder clicking” posts last year as many parts of the world moved into ever-hotter summers. There was a huge spike last year after the Prusa Lack enclosure blog entry was published in April and happy new owners tried using them in hotter months. The causes of excessive heat are varied, and many people have declared victory once they found one solution that worked in their specific circumstance, but it may take fixing several factors to correct the problem.

Contact and feedback

You can find me on the Prusa support forums or Reddit where I lurk in many of the 3D printing-related subreddits. I occasionally drop into the Official Prusa 3D discord server where I can be reached as bobstro (bobstro#9830). You can email me directly at

Last modified Apr 14, 2021. Last build on Apr 14, 2021.