Are you experiencing a bad print quality, under extrusion or is your nozzle clogged? The "Cold Pull" method a.k.a "the Atomic" method is a simple process that will get your printer back to work without changing a nozzle. The method is named after the user MostlyAtomicBob who first introduced the method to the Ultimaker forums.
Step 1 - Unload/Remove the filament
Preheat the nozzle and unload/remove the filament. For easy access, manually move the print head to the front of the machine and remove the bowden tube (the plastic tube) if applicable. Raise the extuder above the bed or lower the bed. Clean the nozzle with a wire brush if needed.
Step 2 - Heat up the nozzle and feed the cleaning filament
Heat the hotend to 250C using the manual controls inside your software. Cut off about 20cm/8inches of filament and straighten it out as much as possible to make it easier to insert. Once the nozzle has reached the set temperature feed the filament into the hot end manually as far as it goes. Apply some pressure and you'll hopefully see some plastic coming out of the nozzle.
If no filament comes out, use the Acupuncture Needles to clean the tip of the nozzle and then continue.
Step 3 - Lower the temperature and remove the filament
Lower the temperature to 50C. While the print head is cooling down continue to push filament down into the nozzle to ensure that it remains primed full of plastic. As the hotend cools down below melting temperature, you will no longer be able to extrude plastic by hand and that's exactly what we want.
Wait until the temperature has reached 50C. This ensures the plastic is completely cool and hard. Set the hotend temperature to 250c and get ready to pull filament out. Immediately after the hotend starts heating, try to remove the filament with a quick pull.
If your printer is a direct drive, depress the extruder pinchwheel lever and pull the filament out.
After removing the filament, check the color and shape of the tip of the filament. You want to get a "plug" at the end that is shaped like the interior of the nozzle and it should be clean.
Repeat step 2 and 3 until the filament comes out completely clean and with the correct shape. Generally, 4 pulls with Nylon will be sufficient.
Step 4 - Assembly
Assemble the bowden tube or any other parts of your extruder/hotend back to its place and your printer is ready to go!