3D Printer Not Extruding? Work Down the Blockage

“Not extruding” covers three different failures with three different causes, and fixing the wrong one wastes an afternoon. Work out which one you have first, then follow that section.

Which Failure Is This?

• Nothing comes out at all. The nozzle is blocked, the filament isn’t being gripped, or the hotend isn’t up to temperature. Start with the next section.
• Something comes out, but it’s thin and gappy. Under-extrusion. Partial blockage, wrong flow, or a hotend that can’t melt fast enough.
• It printed fine for an hour, then stopped. Heat creep or a slowly forming clog. This is the most common and the most misdiagnosed.

Nothing Comes Out At All

Work these in order. The list runs cheapest first on purpose.

1. Check the temperature is actually reached, not just set. A cold hotend extrudes nothing and most firmware refuses to move the extruder below about 170C.
2. Check the filament path. A roll that has tangled or slipped under itself on the spool will hold like a knot. Unwind a metre by hand and check it feeds freely.
3. Check the extruder is gripping. Open the idler and look at the filament: it should have clean knurl marks. Chewed flat means the gear ground a groove instead of pushing. Cut off the damaged section and re-feed.
4. Check idler tension. Too loose and the gear slips. Too tight and it deforms the filament into an oval that jams in the throat.
5. Push filament through by hand with the hotend at printing temperature and the idler released. If it extrudes easily by hand, the problem is the extruder. If it doesn’t, the problem is the hotend.
6. Clear the nozzle. With the hotend hot, feed a 0.4mm cleaning needle up through the tip a few times, then push filament through. If it clears and then blocks again the next print, the debris was higher up: do a cold pull.

Under-Extrusion: Thin, Gappy Walls

The nozzle is producing plastic, just not enough of it. Look for gaps between adjacent lines, top surfaces you can see daylight through, and walls that feel thin.

• Partial clog. The most common cause. Some debris or carbonized plastic is narrowing the orifice. Cold pull.
• Temperature too low. Stiff plastic resists being pushed. Raise the nozzle 5-10C and watch whether the gaps close.
• Printing faster than the hotend can melt. Every hotend has a volumetric flow ceiling. A stock hotend on a 0.4mm nozzle runs out somewhere around 10-15 mm³/s. Fast profiles and larger nozzles both cross it easily. Slow down or raise the temperature.
• Flow rate or E-steps wrong. See below.
• Filament diameter mismatch. A profile set for 2.85mm running 1.75mm filament will under-extrude by an enormous margin. Check the slicer.
• Wet filament. Moisture causes popping and inconsistent flow that looks like under-extrusion. If the nozzle hisses or crackles, dry the spool.
• Partially blocked PTFE tube. On Bowden machines, a tube that has been cut unevenly or has pulled back from the nozzle leaves a gap where plastic collects.

It Starts Fine Then Stops: Heat Creep

The signature is unmistakable once you’ve seen it: the first thirty to ninety minutes are perfect, then extrusion tapers off and the extruder starts clicking. Cool everything down and the filament pulls out with a fat, bulbous plug just above the heatbreak.

Heat is travelling up the hotend faster than the cooler can remove it, so the filament softens in the throat, swells, and wedges itself in a section that was never meant to hold molten plastic.

Causes, in the order worth checking:

• Hotend cooling fan not running or obstructed. The small fan pointed at the heatsink, not the part-cooling fan. Confirm it spins the whole print.
• Enclosure too hot for the material. This is why PLA in a closed chamber jams. Open the door for PLA.
• Nozzle temperature higher than the material needs. Backing off 5-10C often solves it outright.
• Long retractions pulling molten plastic up into the cold zone. Keep direct-drive retraction under about 2mm.
• Poor thermal paste or a loose heatbreak. A heatbreak that isn’t seated tight against the nozzle leaves a gap that fills and cools.
• Ambient temperature. A printer in a hot room in summer is a genuinely different machine from the same printer in winter.

The Cold Pull

The one maintenance procedure that clears most partial clogs without disassembly. Nylon works best; PLA works well enough.

1. Heat the nozzle to printing temperature for whatever material is currently loaded and push new filament through until the colour runs clean.
2. Drop the target to about 90C for PLA, or 120C for nylon, and wait for it to actually get there.
3. Pull the filament out firmly and straight, in one motion.
4. Look at the tip. You want a clean, sharp cone that mirrors the nozzle interior, often with a fleck of debris on it.
5. Repeat until the tip comes out clean.

If three cold pulls don’t clear it, the nozzle is done. They’re consumables; replace it rather than fighting it.

Extruder Clicking or Skipping

Clicking is the extruder motor losing grip and jumping back. It’s a symptom, not a cause: the extruder is being asked to push harder than it can, so find out what’s resisting.

• Blockage or partial clog in the nozzle
• Temperature too low for the flow rate
• Printing too fast for the hotend
• Z-offset too low, so the nozzle is dragging on the bed with nowhere to put plastic
• Idler tension too tight, deforming the filament
• Tangled spool

Check the Z-offset first if the clicking only happens on the first layer. That single case accounts for a surprising share of “my extruder is broken” reports.

Check Flow and E-Steps

If prints are consistently a little thin with no other symptom, calibrate rather than guess.

1. Mark the filament 120mm above the extruder inlet.
2. Command a 100mm extrusion at low speed with the hotend hot.
3. Measure from the mark to the inlet. It should be 20mm.

If 25mm remains, only 95mm actually fed, and the E-steps are 5% low. Correct in firmware, then confirm with a single-wall test cube: slice a hollow cube with one perimeter and no top, print it, and measure the wall with calipers. A 0.4mm nozzle should give roughly 0.42-0.45mm. Adjust the flow multiplier to close the gap.

Prevention

Most extrusion failures are maintenance failures with a delay. Nozzles wear and clog, PTFE liners degrade, heatsink fans fill with dust, and abrasive filament accelerates all three.

Track nozzle hours rather than guessing, keep filament dry, and replace the nozzle before it starts costing you prints. Gyroid counts print hours per printer and schedules nozzle, belt, and lubrication reminders against them, so the consumable that causes half of these failures gets replaced on a schedule instead of after a ruined print.