Gaps in layers, weak prints, clicking extruder — under extrusion has 8 common causes. Start with the most likely one for your situation and fix it in under 10 minutes.
Extruder clicking?
→ Partial clog. Clean feeder gear + do a cold pull.
Consistent thin walls?
→ Flow rate / e-steps. Increase flow by 3-5% in slicer.
Popping / crackling?
→ Wet filament. Dry at 65°C for 4-6 hours before printing.
Signs: Inconsistent extrusion, clicking extruder, gaps that come and go
Fix: Cold pull, then hot pull. Heat to 220°C, push filament manually — feel for resistance. If partial clog: 3-5 cold pulls at 90°C usually clear it.
Signs: Consistent under-extrusion at speed, thin walls, gaps in top layers
Fix: Raise nozzle temp by 5°C increments. Run a temperature tower to find the sweet spot for your brand. PLA may need 210°C vs default 200°C at high speeds.
Signs: Under extrusion at high speed areas, fine at slow infill
Fix: Reduce outer perimeter speed to 40-50mm/s. The hot end has a max volumetric flow rate — exceeding it causes under extrusion regardless of temperature.
Signs: Clicking sound from extruder, filament ground down at feeder gear
Fix: Clean feeder gear with a stiff brush (filament dust fills gear teeth). Check tension spring. If Bowden: check tube for filament drag. If direct drive: check motor current.
Signs: Consistent under-extrusion across all speeds, all areas
Fix: Calibrate e-steps: mark 100mm of filament, command 100mm extrusion, measure what actually fed. Adjust steps-per-mm. Or increase flow rate in slicer (start at 100%, try 103-105%).
Signs: Popping/crackling sounds, steam visible, rough surface, inconsistent extrusion
Fix: Dry filament at 65°C for 4-8 hours (PLA/PETG), 75°C for Nylon. Use a food dehydrator or filament dryer. Moisture causes steam micro-bubbles that interrupt flow.
Signs: Under extrusion after retraction moves, filament snags
Fix: Disassemble cold end of hot end. Push Bowden tube fully into coupling while hot end is at temp — it must seat flush against nozzle with zero gap. PTFE gap creates filament blob that causes clogs.
Signs: Consistent thin walls, all areas under-extruded equally
Fix: Check slicer nozzle diameter setting matches physical nozzle. If you changed from 0.4mm to 0.6mm nozzle, update the slicer setting or flow math is wrong.
A cold pull is the most effective way to clear partial nozzle clogs — it pulls out the debris plug instead of pushing it deeper.
Heat to printing temp
Set nozzle to 220°C (PLA) or 240°C (PETG). Push filament manually until it flows freely — confirms the nozzle is fully heated.
Push cleaning filament through
If available, use nylon or PLA at this step — they grip debris better than PETG. Push a 20cm length through slowly.
Cool to pull temp
Set nozzle to 90°C (PLA), 110°C (PETG/ABS). Wait for target temp — the filament solidifies while shaped by the nozzle interior.
Pull firmly
With the nozzle at pull temp, grip the filament and pull steadily upward with consistent force. It should come out as a solid plug shaped like the nozzle interior.
Inspect and repeat
The tip of the pulled filament should show the nozzle bore shape. Dark residue or uneven tip means more pulls needed. Repeat 3-5 times until tip comes out clean.
Test extrusion
Reheat to printing temp, extrude 20-30mm. Flow should be smooth and consistent. If still clicking, the clog may need a needle + hot pull or nozzle replacement.
If under extrusion is consistent across all print areas and all speeds, the issue is likely flow rate calibration — not a clog.
Print a single-wall cube
Slice a 20×20×20mm cube in "vase mode" (spiral/single wall). Set line width = nozzle diameter (0.4mm). Print at normal speed.
Measure wall thickness
Use digital calipers to measure the wall. It should be very close to 0.4mm (your nozzle size). Measure at multiple points.
Calculate correction
If measured = 0.38mm but expected 0.40mm: correction = 0.40/0.38 = 1.053 → increase flow by 5.3%. In Cura: set Flow % to 105. In PrusaSlicer: set Extrusion Multiplier to 1.053.
Confirm with a second print
Print again with the adjusted flow. Wall should now measure ~0.40mm. Repeat if still off.
| Material | Most Common Cause | Primary Fix |
|---|---|---|
| PLA | Partial clog, temp too low at high speed | Raise temp 5°C, reduce speed to 60mm/s for troubleshooting. Cold pull if clog suspected. |
| PETG | Temp too low, retraction too high, heat creep | Min 235°C. Check heat break cooling fan. Reduce retraction to 1-3mm (DD). |
| ABS | Speed too high, heat creep, moisture | 245°C+, slow first layer, ensure enclosure temp is stable. Dry if stored. |
| TPU | Speed too high, extruder grip slipping on flex | Max 25mm/s. Zero retraction (or 0.5mm). Only direct drive. TPU compresses if forced. |
| Nylon | Moisture (most likely), temp too low | Dry 8-12h at 75°C IMMEDIATELY before printing. 250-265°C nozzle. Enclosure. |
| CF composites | Partial clog (abrasive), hardened nozzle worn | Hardened steel nozzle required. Check nozzle wear — CF grinds brass in 5-10 hours. |
• Gaps between perimeter lines
• Holes in top surface infill
• Weak, brittle layers that separate
• Visible layer lines with missing material
• Clicking/grinding extruder noise
• Blobby, rough surface
• Dimensions larger than expected
• Strings between walls
• Nozzle drags through previous layers
• "Elephant foot" on first layer