Hotend and nozzle maintenance

Note

These notes apply to the Prusa i3 Mk3 printer. If you are using a different printer, please verify the hardware details are same. These pages may be a bit rough as I revise them and add new material. Please check back regularly for updates.

This page describes the “cold pull” method of clearing the nozzle and hotend of built-up filament and gunk that can accumulate over the course of printing. This is a very simple procedure that can avoid a lot of headaches with jams, clogged nozzles and under-extrusion. It also helps cleaning accumulated bits of filament that can drop into your ongoing prints.

With regular cleaning using the procedure, I’m able to swap freely between PLA, PETG, NGEN, XT and a variety of carbon, wood, copper and other filled materials with no issues. Example extremes would be switching from 3DXTech PETG that prints at 265C to PLA at 200C.

I recommend a cold pull in the following situations:

  • When switching between material types, particularly from high-temp (e.g. ABS) to low-temp (e.g. PLA), stray material can build-up in the nozzle, causing jams and under-extrusion.
  • Before removing a nozzle for storage to avoid having to worry about what material was last printed.
  • As part of regular maintenance keep the nozzle and hotend clear.
  • If you begin to experience uneven extrusion using settings that worked previously.

One sure indicator that it’s time for a cold pull is to try the following:

  1. Raise Z to max.
  2. Heat the nozzle to printing temperature.
  3. Extrude some filament and examine the flow out of the nozzle.

If the flow pulls to one side, you may have a partial hotend or nozzle clog that a cold pull may remedy.

Required tools

  1. 2.5mm hex wrench (included with printer) or ball hex wrench (recommended)
  2. Soft brass wire brush (recommended)
  3. Cleaning filament (ABS or special cleaning filament – eSun cleaning filament recommended)

Preparing for the cold pull

It’s a good idea to prepare things for doing the cold pull to avoid repeating steps.

  1. Heat hotend to whatever temp the currently-loaded material prints at.
  2. Eject the currently-loaded material. Put a clip on the filament and spool to avoid tangles, and store it away.
  3. Raise Z to max. Press and hold the front knob until it chirps, then rotate it to lift the Z axis. Push the knob again when done.
  4. Heat hotend to a temp higher than normal printing temps (e.g. 260C). The goal is to melt any material you might have used previously, so be sure to use a high setting.
  5. As you wait for things to heat up, clean the nozzle and hotend using a soft brass wire brush. Give the hotend a light scrubbing, being careful to avoid the thermistor and heater cartridge wires that protrude from the left side as viewed from the front of the printer. You want to remove any built-up filament and other gunk that has built up before it starts dropping into your prints.
  6. Load either ABS (white recommended) or cleaning filament. I personally use eSun cleaning filament and really like the results.
  7. Let material stream through to clean the hotend out. I usually answer “N” twice to the “is the filament loaded?” question to make sure the hotend and nozzle are full of cleaning filament. As the molten cleaning material flows through the hotend it will pull away burnt filament and crud from prior prints.
  8. Reset the printer with the button below the knob on front to reset the temperature.
  9. Let the hotend cool with your cleaning material filling the hotend and nozzle. As the material cools, any accumulated crud will be trapped in the cleaning filament.
  10. While it’s cooling, loosen the extruder tensioning screws on the left of the extruder housing to avoid putting stress on the extruder motor in the following steps.

Performing the cold pull

Now we’re ready to do the actual cold pull. The hotend has cooled with the cleaning material melted in the heat block. With any luck, any left-over filament and build-up has melted into the cleaning material and is now trapped. We want to remove the material to pull out the debris.

  1. Let the hotend cool to below 90C.
  2. Set the temp to a high temperature (260C).
  3. Watch the hotend temp. When it gets up near 90C, grab the cleaning filament with pliers and brace the extruder with your other hand.
  4. When the temperature reaches 90C, pull firmly and steadily straight up. Don’t jerk it, you want the filament to stretch and pull out without breaking. The material should be soft but not molten.
  5. As you pull it up, the material should be warm enough to be slightly elastic, so should pop out.

Inspect the pulled filament and you should see the shape of the hotend interior. If you performed the pull at a cool enough temperature, it should not be distorted. If the pulled strand is stretched, try starting to pull at a cooler temperature.

You may see loose bits of other filament that dislodged. If so, reload cleaning filament, reset to let the hotend cool and repeat this process. You may have to push cleaning filament through manually if extruder tension screws are still loose.

Finishing up

Once the pulls come out clean, you can continue on as normal.

  1. Re-tighten the extruder tension screws to < 1mm above the cover. (I always forget this step.)
  2. Heat the nozzle up to your next desired material temp.
  3. Load your next material.

Contact and feedback

You can find me on the Prusa forums or Reddit where I lurk in many of the 3D printing-related subreddits.

Last updated on Oct 23, 2018