Cold pull (MK4, XL)

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A '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. You can also use it to clean your hotend during your usual maintenance routine.

The cold pull should be done if your nozzle is only partially clogged, and some filament is still being extruded. If the nozzle is completely clogged, please check the clogged hotend article for MK4, or the clogged hotend article for XL.

Preliminary steps for XL

On the Original Prusa XL, proceed with these two steps before the cold pull procedure.

1. Insert a piece of filament into the side PTFE tube, just enough to trigger the side filament sensor. 
2. Unscrew the Bowden PTFE tube above the extruder.

Cold pull procedure

1. Load a piece of PLA filament in the extruder, inserting it from above the extruder. The printer will prompt a material selection: select PLA and complete the loading procedure. 
2. Open the Idler Swivel.
   

   Original Prusa MK4	Original Prusa XL

3. Go to LCD Menu -> Control -> Temperature -> Nozzle Temperature and set the temperature to 270 °C.
4. Once it has reached 270 °C push the PLA filament in until it starts pouring out of the nozzle.
5. Stop heating by pressing Cooldown in the LCD Menu -> Control -> Temperature -> Cooldown, or by pressing the reset button. 
6. 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.
7. Pick away any extruded material from the nozzle so there is nothing obstructing the pull later on.
8. Wait for the temperature to reach 100 °C. As soon as it reaches 100 °C, grab the filament with pliers and pull it slowly but steadily out of the extruder. Make sure to pull straight upwards, not sideways, or the filament can break inside. Hold the extruder with your other hand.
9. Don't stop until the filament is completely pulled out from the extruder.

Results

On the tip of the filament that has been pulled out, you may see remnants of the previous material(s) you have been using or some burnt dirt that has settled in the nozzle (left picture). You might want to repeat this procedure several times until the filament comes out clean.

The right picture shows 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 the nozzle was filled and nothing was left inside. Also, the color is not mixed with the one you have been using previously or has dark marks on it.

After the procedure, close the Idler and the Idler Swivel.