Cold Pull: How to Clean a Dirty Nozzle Before It Clogs Completely

What this technique does and when it's the right move

A cold pull means melting filament into the nozzle, letting it cool, then pulling it out in one steady motion. As it comes out, the tip brings along whatever was stuck inside, such as leftovers from an old material or burnt-on residue. Prusa's documentation describes it as a way to clean both the nozzle and the hotend, and says it also fits into a regular maintenance routine.

Timing matters. According to Prusa, you should reach for a cold pull when the nozzle is only partially clogged and some filament still comes out. A fully blocked nozzle calls for a different fix, covered in our clogged nozzle guide. The usual warning signs are uneven flow, skinny layers, or extrusion that weakens for no obvious reason. Those symptoms have other possible causes too, so rule out the common sources of under-extrusion first. If the nozzle still looks like the prime suspect, act now, because this method is off the table once nothing gets through.

Picking your filament and getting set up

Prusa says PLA works best. Other filaments don't hold the tip shape the same way, and they either tear or melt too much. The company also notes that some filaments are made specifically for cleaning hotends. Even if you mostly print PETG or ABS, it's worth keeping a length of PLA around for this job. An end-of-spool scrap works as long as there's enough of it, since Prusa asks for at least 30 cm for the automatic routine.

Have a pair of pliers ready too. Prusa uses them for the pull itself, and on the CORE One they can also help you push filament down. You'll need access to the top of the extruder. On the XL, temporarily unscrew the fitting above the Nextruder. On the CORE One, push up the bowden bend and unscrew the metal fitting. Take your time, because the nozzle stays hot for much of the process. Keep your fingers away from the hot end and let the pliers do the work.

The manual pull, step by step

Prusa lays out a very similar sequence for the XL before firmware 6.1.3, the MK4/MK3.9 before firmware 5.1.3, and the CORE One. On the CORE One, start by turning off Filament Sensing in the settings. Load a piece of PLA from above the extruder and choose PLA when the printer asks for a material. Then set the nozzle to 270 °C. Once it gets there, push the filament in until it starts pouring out of the nozzle, then stop heating with the Cooldown option.

Keep pushing by hand as the nozzle cools, until the PLA can no longer melt and come out. Prusa puts that at around 170 °C. Don't skip this part, because the nozzle has to be full for the pull to work. Next, pick away anything hanging from the nozzle. When the temperature hits 100 °C, grab the filament with pliers and pull slowly but steadily, straight up, until it's completely out. Hold the extruder with your other hand. Pulling sideways can snap the filament inside.

Prusa's automatic routine on newer printers

On several Prusa machines, the firmware handles the fiddly part for you. Prusa's documentation lists firmware 6.0.0 for the MK4/S and MK3.9/S and firmware 6.1.3 for the XL, and it describes the same mode on the CORE One and CORE One L. You'll find it under LCD Menu, Control, Cold Pull. On the MK4/S and MK3.9, the screen lets you unload the current filament, load PLA, or continue with what's loaded. Only pick that last option if PLA is already in the printer.

If the nozzle is hot, the printer waits for it to cool to 36 °C, heats to 80 °C, and unloads the filament at that temperature. All that's left is pulling the filament out by hand, going upward. You may feel slight resistance, and if it's stuck, open the idler lever. On the XL, unload the filament, press down the blue part of the fitting, pull out the PTFE tube, then load PLA directly into the Nextruder. These numbers apply to the Prusa models named here. On any other brand, follow the manufacturer's instructions.

Reading the filament tip and deciding whether to go again

Think of the filament tip as a quick readout of what's inside your nozzle. Prusa says you may see remnants of earlier materials or burnt dirt that had settled in there. If you do, run the procedure again. The documentation notes that several rounds may be needed before the filament comes out clean, so there's no magic number to hit. Let the tip make the call.

According to Prusa, a good tip has two traits. First, it carries the imprint of the nozzle, which confirms the nozzle was full and nothing stayed behind. Second, its color isn't mixed with the material you used before, and it has no dark marks. If the imprint is missing, the nozzle probably wasn't full, so focus on pushing during the cooldown next time. A light-colored PLA makes dark deposits easier to spot. When the tip looks clean, run a short print and check whether the flow has evened out.

When cleaning isn't enough

If several pulls give you a clean tip but extrusion is still weak, the nozzle probably isn't the problem anymore. Look elsewhere: the filament, the extruder, your settings. If nothing comes out at all, a cold pull no longer fits, since Prusa reserves it for nozzles that are still extruding. Switch to your printer's unclogging procedure and don't force the filament through.

Cleaning won't bring back a worn or damaged nozzle. If the same trouble returns after every cleanup, swapping the nozzle becomes a reasonable next step. To stay ahead of clogs, add the cold pull to your regular maintenance, as Prusa suggests, rather than waiting for a full blockage. Good times to run one include after a material change or at the first sign of uneven flow. Also check the condition of your spool. Old or damp filament can act a lot like an early clog, so rule it out before you start taking hardware apart.

Sources and limits

• Prusa Knowledge Base — Cold pull (MK4S/MK4/MK3.9S/MK3.5S/XL)
• Prusa Knowledge Base — Cold Pull (CORE One / CORE One L)

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.