Cold pull

Updated 3 weeks ago ​by Martin Lexa

The cold pull is a technique that allows you to clean your printer’s nozzle and hotend from any material that may be stuck or burnt inside. Besides being helpful when the extruder doesn't extrude any filament, you may use it to clean your hotend during your usual maintenance routine.

If you have the MMU2S (or still the MMU2), unscrew the PTFE tube that connects the MMU unit with the extruder.

The best filament to use for the following procedure is probably nylon because of its strength, however, we get the same nice results with PLA, which is also cheap and commonly available. On the internet, you can even get a special filament made for hotend cleaning. It works but tends to be expensive, so we leave it up to you to see if it's worth trying.
  1. Go to the LCD Menu -> Settings -> Temperature -> Nozzle and set the temperature to 275 °C.
  2. While waiting for the nozzle to reach the temperature, toggle the Filament autoload off in the LCD Menu -> Settings -> F. autoload.
  3. Still being in the Menu, go to Settings and choose Disable steppers.
  4. Open the Extruder Idler door.
    1. If you have an MK2/S, unscrew both M3x40 screws with springs, the door should then open by itself.
    2. If you have an MK3 or an MK2.5, unscrew both M3x40 screws under the hexagonal window (they also have springs on them).
    3. If you have an MK3S or an MK2.5S, unscrew the single M3x40 screw (also with a spring).
If you see a piece of filament stuck in the PTFE tube, see the section "Filament stuck in the PTFE tube" in this guide.
  1. Insert a PLA filament manually into the extruder (it is possible as soon as the hotend temperature is above 215 °C) and push it in until it starts pouring out of the nozzle.
  2. Cancel the heating by pressing Cooldown in the LCD Menu -> Preheat (scroll all the way down), or by pressing the reset (X) button. Let the nozzle temperature drop to the room temperature.
  3. Continue manually pushing the filament down until the temperature is too low for it to melt and come out (around 170 °C for PLA). The nozzle has to be filled for the cold pull to be successful.
  4. After the nozzle cools down to the room temperature, go again to the LCD Menu -> Settings -> Temperature -> Nozzle and set the temperature to 85 °C. (If you are using nylon, set it to 65 °C.)
  5. As soon as the extruder reaches this temperature, grab the filament with pliers and pull it slowly but steadily out of the extruder.
  6. Don't stop until the filament is completely pulled out from the extruder.
Be careful! The filament can break inside. Make sure to pull straight upwards, not sideways. Hold the extruder with your other hand.
  1. On the tip of the filament that has been pulled out, you might see remnants of the previous material(s) you have been using or some burnt dirt that has settled in the nozzle. You might want to repeat this procedure several times until the filament comes out clean.

This is what a clean cold-pulled filament should look like. It is important to have the imprint of the nozzle on it, this way you are sure that nothing was left inside. Also the color is not mixed with the one you have been using previously.

At the end, we recommend running the Z calibration (Menu -> Calibration -> Calibrate Z) as pushing on the extruder might have thrown it off balance.
Please see this article to learn about most common causes leading to filament extrusion problems and how to prevent them from happening.

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