3D Printers: Fixing a Blocked Hot-End or Extruder

By Richard Horne, Kalani Kirk Hausman

When your 3D printer’s hot-end gets blocked or your extruder’s filament drive fails, the warning signs are usually obvious. The stream of plastic starts to lessen and then stops; the printer keeps trying to print but extrudes layer after layer of nothing.

The first things to do are stop the printer and ensure that the heater block on the hot-end is still at the expected temperature. (Ideally, for maximum safety, you should use a noncontact laser temperature sensor.) If the heater temperature is significantly below 160 degrees C, the heater used in the hot-end or temperature sensor may have failed, or the wiring or electronics controlling the heaters may have developed a problem.

Unfortunately, wires commonly break — and insulation wears away — on a home 3D printer due to the constant movement of the machine. Wiring should always have plenty of room to move around gently, with enough slack — not tightly bent or yanked back and forth as the machine moves. Using silicon-coated wire can help, especially if it has extra resistance to heat. Increasingly, new machines use gently curved ribbon cable — a ribbon of many parallel wires instead of a single thick wire — which tends to alleviate cable strain and damage.

If your heater block is jammed but is at the expected temperature, follow these general steps to clear the jam:

  1. Keep the heater block turned on.
  2. Make sure that the filament drive isn’t blocked and that the filament isn’t buckled or wrapped around the extruder drive wheel.

    If you think you may have a blockage, follow the steps here. If you have buckled filament wrapped around the drive wheel, first remove the buckled filament, and then follow the next steps to check if the cause of the buckle was a blockage.
  3. Release the idler bearing, and gently pull out the filament.

    A filament rarely gets so jammed that it can’t be pulled out while the hot-end is at temperature. More commonly, the removed filament shows signs of being overly compressed — a little fatter where it melted inside the hot-end. Usually, pulling out the melted filament removes contaminants from the hot-end nozzle.
  4. Cut off the melted filament end, and push it into the hot-end.

    If you can push down, and material is extruded from the nozzle, you’ve cleared the blockage. Otherwise, proceed to Step 5.
  5. If you can’t get the material to extrude, allow the end of the material to melt, and pull it out again.

    Repeating this step several times should clear most blockages. If not, proceed to Step 6.
  6. If you still have a blockage, do either of the following things (extremely carefully):
    • Push a pin or small drill bit into the nozzle end while pulling out the melted filament.
    • Allow the hot-end to cool, and when it’s cool, use a chemical solvent (such as acetone) to dissolve any buildup.

Before using any chemical cleaner, check with the supplier, and mention the type of material that you were using in the hot-end when the jam occurred.

You may be starting to think that having a few extruders is a good idea — and usually, it is. In the event of a blockage, a backup extruder can get you printing again while you repair. Another reason for having a choice of extruders is that your machine becomes much more capable of printing different types of objects, which can widen your selection of available printing materials.