Quick Solution (TL;DR)
Under-extrusion is usually caused by partial nozzle clog, low temperature, or incorrect E-step value. First step: increase nozzle temperature by 5-10°C. If it doesn't fix it, perform E-step calibration.
What is Under-extrusion?
Under-extrusion is a condition where the printer extrudes less filament than it should. Result: thin walls, visible gaps, weak layer adhesion, and brittle prints.
Symptoms
- Walls are thinner than they should be
- Gaps between infill lines
- Weak layer adhesion (can be broken by hand)
- Top surface is not fully closed (looks holey)
- Print is generally weak and brittle
8 Common Causes and Solutions
1. 🔥 Low Nozzle Temperature
If the temperature is insufficient, the filament cannot melt properly, and the flow decreases.
Solution Steps:
- Increase nozzle temperature by 5-10°C
- Perform a temperature tower test
- Try the upper limit of the filament manufacturer's recommended range
Filament-Based Recommendations:
| Filament | Minimum | Recommended | Maximum |
|---|---|---|---|
| PLA | 190°C | 205-215°C | 230°C |
| PETG | 220°C | 235-245°C | 260°C |
| ABS | 220°C | 240-250°C | 270°C |
| TPU | 210°C | 225-235°C | 250°C |
2. 🧹 Partial Nozzle Clog
The nozzle is not completely clogged, but there are residues inside. Filament passes through, but the flow is restricted.
Symptoms: Sometimes normal, sometimes low extrusion. Irregular lines.
Solution Steps:
- Cold Pull (Atomic Pull): Heat nozzle to 250°C → push filament → reduce to 90°C → pull out quickly
- Repeat 3-5 times (if the extruded filament is clean and pointed, the clog is gone)
- Clean the nozzle tip with a cleaning needle (0.3-0.4mm)
- If the problem persists, replace the nozzle
3. ⚙️ Incorrect E-step Calibration
If the E-step value, which defines how much filament the extruder motor should push per step, is incorrect, it will lead to constant under- or over-extrusion.
E-step Calibration Steps:
- Mark the filament 120mm above the nozzle entry
- In the terminal:
G1 E100 F100(command to push 100mm of filament) - Measure the remaining distance. Example: if 15mm remains, it means 105mm was pushed
- Read the current E-step value:
M503→ look at theM92line - New value = Current E-step × (100 / Actual measurement)
- Save:
M92 E[new_value]→M500
Example Calculation:
- Current E-step: 93
- Desired: 100mm, Actual: 95mm
- New = 93 × (100/95) = 97.89
4. 📏 Incorrect Filament Diameter Setting
If the filament diameter is set to 2.85mm in the slicer, but you are using 1.75mm filament, the printer will push too little filament.
Solution:
- Check the filament diameter in the slicer
- Cura: Settings → Material → Diameter: 1.75
- PrusaSlicer: Filament Settings → Filament → Diameter: 1.75
- Measure the actual filament diameter with digital calipers (from 3 different points)
- Enter the average value into the slicer (e.g., 1.73mm)
5. 🦷 Worn Extruder Gear
The extruder gear wears out over time and becomes unable to grip the filament.
Symptoms:
- A "click-click" sound comes from the extruder
- Indentations/gouges on the filament
- Accumulation of filament dust
Solution Steps:
- Remove and inspect the extruder gear
- If the teeth are flattened, install a new gear
- Upgrade to a hardened steel or dual-gear extruder instead of a brass gear
- Check the gear tension — too tight crushes the filament, too loose cannot grip
6. 🔄 Bowden Tube Issue
If there is play, bending, or wear in the Bowden tube, filament resistance increases.
Solution Steps:
- Remove the Bowden tube and check it on a flat surface
- Ensure the inner diameter is uniform (filament should slide easily)
- Ends must be clean and cut straight — use a Capricorn tube cutter
- The tube must seat properly in the hotend — gaps can lead to clogs
- Switch to a Capricorn PTFE tube (tighter tolerance, less friction)
7. 💨 Insufficient Cooling (Heat Creep)
Overheating of the upper part of the hotend melts the filament prematurely and causes clogs.
Symptoms: Problems start on long prints. Normal for the first 1-2 hours, then decreases.
Solution Steps:
- Check if the hotend fan (small fan) is working
- Verify that the heat break is clean and properly installed
- Replace thermal paste
- If using an all-metal hotend, keep retraction distance at 1-2mm
- If the ambient temperature is too high (35°C+), add an extra fan
8. 🌀 Low Flow Rate
If the flow rate in the slicer is too low, under-extrusion will occur.
Solution Steps:
- Check the flow rate — default should be 100%
- Print a test cube: single wall, 0.4mm nozzle → wall thickness should be 0.4mm
- If the measurement is 0.36mm: New flow = 100 × (0.4/0.36) = 111%
- Adjust flow based on filament (PETG usually needs 95-98%)
Quick Diagnosis Flowchart
- Is temperature correct? → No → Increase by 5-10°C
- Does cold pull come out clean? → No → Clean/replace nozzle
- Is E-step calibrated? → No → Perform E-step calibration
- Is extruder making clicking sounds? → Yes → Check gear and tension
- Is Bowden tube properly seated? → No → Replace tube
- Does it happen on long prints? → Yes → Check for heat creep
Prevention Tips
✅ Perform temperature tests with every new filament spool ✅ Check E-step calibration every 6 months ✅ Replace the nozzle every 500 printing hours (brass nozzle) ✅ If using a hardened steel nozzle, increase temperature by 5-10°C ✅ Store filaments in a dry environment
Frequently Asked Questions
Q: What if under-extrusion occurs only on specific layers? Most likely a partial clog or filament quality issue. Try a cold pull and a different filament.
Q: I installed a new nozzle, but still have under-extrusion? Perform E-step and flow rate calibration. Also, verify that the new nozzle is the correct size.
Q: I'm constantly experiencing under-extrusion with PETG? PETG requires a higher temperature (235-245°C). Also, reduce the printing speed by 10-15% compared to PLA.