Extruder Clicking or Skipping

Likely causes, most common first

1. Partly or fully clogged nozzle or hotendMost common
   Prusa says the clicking is the motor suddenly needing more force than a preset threshold and skipping one or more steps. A clog is the usual source of that extra resistance. See Nothing Coming Out of the Nozzle.
2. Nozzle too cold for the flowCommon
   Colder plastic is thicker and harder to push. Prusa suggests raising the hotend temperature by 5 to 15 °C Starting point, checked against the range for your filament.
3. First layer too close to the bedCommon
   Prusa says a first layer set too close can eventually clog the hotend.
4. Idler tension wrongCommon
   Prusa notes an overtightened idler stops the gears from pushing properly, and its heat creep guide adds that too loose lets the gears slip and too tight lets the teeth grind and choke the filament.
5. Dirty or misaligned drive gearsOccasional
   Prusa says to clear leftover plastic from the gears and check they line up with the filament path. Bambu Lab lists clicking or grinding noises and visible debris in the gears as reasons to clean its extruders.
6. Heat creepOccasional
   Prusa's heat creep guide lists the extruder grinding filament with a clicking or ticking sound as a symptom, with extrusion stopping partway through a print.
7. Blocked filament path or hotend assembly faultLess common
   Prusa lists a PTFE tube jammed with debris and a crooked heater block or nozzle. It also notes clicking can have mechanical, electrical or software causes.

Fix it, one change at a time

1. Unload the filament. If it is ground through and will not unload from the menu, follow your printer maker's manual removal guide.
2. Re-slice with current profiles for your printer and filament, as Prusa suggests, to rule out a bad setting or a damaged model file.
3. Raise the nozzle temperature a little within the filament's printed range, or slow the print down, and retest. If clicking only happens on fast sections, see Gaps, Thin Lines and Weak Walls (Under-Extrusion) for finding your flow limit.
4. Check the first layer height if the clicking happens on the first layer. Raise the nozzle slightly with Z offset or live adjust, or run your printer's first layer calibration.
5. Check for a clog by extruding in the air. If the strand curls or nothing comes out, follow your maker's unclogging procedure from Nothing Coming Out of the Nozzle. The nozzle can cause severe burns; heat it only from the printer's menu.
6. Set the idler tension and clean the gears. Power the printer off and unplug it first: Bambu Lab says to disconnect power before extruder maintenance. Clear plastic dust from the gear teeth as your maker describes and return the idler to its default tension.
7. Check the filament path above the hotend, such as the PTFE tube, for debris or a kink.
8. Rule out heat creep if clicking starts partway through prints. See Extrusion Stops Partway Through a Print.

Confirm it is fixed

Load fresh filament and extrude a long length in the air at normal temperature: it should feed smoothly with no clicks. Then print a part with long, fast infill sections and listen through the whole print. Pull a short length back out afterward; the gear marks should be shallow and even, with no bitten section.

Why it happens

The extruder is a small stepper motor driving a toothed gear that grips the filament and pushes it into the hotend. The motor has a limit to how hard it can push. When the plastic ahead of it cannot move as fast as the motor is turning, because the nozzle is narrowed, the plastic is too cold and thick, or the nozzle is pressed against the bed, the pressure rises until the motor slips back by a step. That slip is the click. Prusa describes it as the motor jumping back one or more steps to relieve the pressure.

Each slip lets the gear teeth spin against the same spot of filament, which grinds a notch into it. Once the notch is deep enough, the gear has nothing to grip and extrusion stops entirely, even if the original resistance goes away. That is why a print can go from a few clicks to no extrusion at all, and why you should unload and inspect the filament before restarting.

Raising the idler tension to stop the slipping treats the symptom: the gears then bite harder and grind the filament faster. Find the resistance first. For how extruder layout affects this, see Direct Drive versus Bowden.