3D Print Troubleshooting: Symptoms, Causes and Fixes

Most 3D printing problems have a handful of causes, and one or two of them are behind the large majority of cases. This guide takes the common FDM faults one at a time: what you see, what usually causes it (most likely first), and what to do about it. Work down the list and change one thing at a time, so you know which fix worked.

Start Here: Five Checks That Fix Many Problems

Before chasing a specific fault, rule out the basics. A surprising number of problems trace back to one of these.

1. Wet filament. Many filaments absorb moisture from the air. Nylon, TPU and PETG are especially prone, and PLA is affected too over time. Wet filament pops and hisses at the nozzle, strings, and prints with a rough, bubbly surface. Dry it in a filament dryer or oven at the maker's recommended temperature.
2. First-layer height (Z offset) and bed level. If the first layer is wrong, everything above it suffers. Tune it until the first layer lines are slightly squashed and just touching each other.
3. Temperature. Print within the range on the spool, then fine-tune with a temperature tower.
4. A worn or partly blocked nozzle. Brass nozzles wear, especially with glow-in-the-dark, carbon-fibre or wood-filled filament. Nozzles are cheap; replacing one is a quick test.
5. Loose belts, wheels and screws. Many motion faults come from something that has worked loose.

Quick Diagnosis Table

Stringing

Symptom: fine hairs or cobwebs between separate parts of the print, where the nozzle travelled across open space.

Causes, most likely first

1. Wet filament. Moisture turns to steam in the nozzle and pushes plastic out while travelling. PETG and TPU are the usual suspects.
2. Temperature too high. Hotter plastic is runnier and oozes more.
3. Retraction distance or speed not tuned. Bowden setups generally need much more retraction than direct-drive extruders.
4. Slow travel moves give the nozzle more time to ooze.

Fixes

• Dry the filament first. If the stringing stops, nothing else needs changing.
• Print a temperature tower and use the coolest temperature that still gives strong layers.
• Use the Retraction Settings tool for a starting distance and speed for your extruder type, then print its retraction test tower.
• Turn on "avoid crossing perimeters" or "combing" in your slicer so travel moves stay inside the part, and raise travel speed if your printer can handle it.

Some light wisps on PETG are normal and brush off with a quick pass of a heat gun.

Warping and Corners Lifting

Symptom: the corners or ends of the print curl up off the bed, often getting worse as the print grows.

Causes, most likely first

1. Plastic shrinking as it cools. ABS, ASA and nylon shrink much more than PLA. Large flat parts with sharp corners are worst.
2. Poor first-layer adhesion (see the next section).
3. Drafts and cold air cooling one side of the part faster than the other.
4. Too much part-cooling fan for the material.

Fixes

• Fix the first layer first: clean bed, correct Z offset, right bed temperature for the material.
• Add a brim, or "mouse ears" (small discs at the corners).
• For ABS and ASA, use an enclosure and little or no part-cooling fan. Keep the printer away from open windows and doors.
• Round off sharp corners in the design where you can.

Poor Bed Adhesion

Symptom: the first layer drags around, does not stick, or the print pops off partway through.

Causes, most likely first

1. Nozzle too high. The plastic is laid on the bed in round strands instead of being pressed on.
2. Dirty bed. Finger grease is the most common culprit, especially on PEI sheets.
3. Bed not level, or not flat. One area sticks and another does not.
4. Wrong bed temperature for the material, or a first layer printed too fast.

Fixes

• Lower the Z offset in small steps until the first-layer lines are slightly flattened and fuse together with no gaps.
• Wash a PEI sheet with warm water and washing-up liquid, or wipe it with isopropyl alcohol. Do not touch the surface afterwards.
• Run bed levelling or a bed mesh. Paste the mesh into the Bed Mesh Visualizer to see whether the bed is warped or just out of level, and how far to turn each screw.
• Slow the first layer down and turn the fan off for it.

Under-Extrusion

Symptom: gaps between lines, thin or weak walls, missing layers, a spongy top surface or a print that looks "starved".

Causes, most likely first

1. Partial clog or a worn nozzle.
2. Printing too fast or too cold for the hotend to melt plastic quickly enough. Every hotend has a maximum volumetric flow.
3. Extruder slipping: worn or dirty drive gear, wrong tension, or a tangled spool.
4. Flow rate or e-steps set low.
5. Wrong filament diameter in the slicer (1.75 vs 2.85 mm).

Fixes

• Clear or replace the nozzle (see Clogs).
• Slow down or raise the temperature by 5 to 10 °C and see if it improves. If it does, you were over the hotend's melt limit.
• Check the drive gear for plastic dust and the spool for snags.
• Check extruder e-steps with the Steps per mm Calculator: mark 120 mm of filament, ask for 100 mm, and measure what is left.
• Then fine-tune flow (extrusion multiplier) with the Flow Rate Calibration tool.

Over-Extrusion

Symptom: walls bulge, top surfaces look lumpy or ridged, holes come out too small and parts are oversize.

Causes, most likely first

1. Flow rate too high for this filament. Different brands and colours often need slightly different flow.
2. E-steps set too high.
3. Filament diameter in the slicer set smaller than the real filament.

Fixes

• Calibrate e-steps first, then flow. Doing it in that order means flow only covers differences between filaments.
• Use the Flow Rate Calibration tool with a single-wall cube measured by calipers, or a flow test pattern, and save the result in each filament profile.
• Measure filament diameter in several places along the spool.

Layer Shifts

Symptom: the print suddenly steps sideways at one layer, so the top half is offset from the bottom.

Causes, most likely first

1. The nozzle hit the print: curled-up edges or an overhang knocked the head and the motor skipped steps.
2. Loose belt or pulley grub screw.
3. Speed or acceleration too high for the motors.
4. Stepper motor or driver overheating, or a binding axis.

Fixes

• Fix curling and warping, turn on Z-hop for travel moves, and check that overhangs are cooling properly.
• Tighten belts to a firm, twangy tension and check the pulley grub screws are tight on the flat of the motor shaft.
• Move each axis by hand with the motors off. It should glide with no tight spots.
• Lower travel speed and acceleration and see if the shifts stop.

Elephant's Foot

Symptom: the bottom few layers bulge outwards, so the base of the part is wider than the rest.

Causes, most likely first

1. Nozzle too close on the first layer, squashing it out sideways.
2. Bed too hot, so the lower layers stay soft under the weight above.

Fixes

• Raise the Z offset slightly.
• Drop the bed temperature by 5 °C at a time.
• Use your slicer's elephant's foot compensation, or add a small chamfer to the bottom edge of the model.

Z-Banding (Horizontal Ridges)

Symptom: regular horizontal ridges or bands up the side of the print, repeating at a fixed spacing.

Causes, most likely first

1. Layer height not a whole number of Z motor steps. Some layers get rounded up and some down.
2. Lead screw wobble: a bent screw, a misaligned coupler, or a stiff Z axis. The ridge spacing usually matches the lead screw pitch (often 8 mm on a common T8 screw).
3. Bed temperature swinging with bang-bang control, which makes the bed expand and shrink slightly.
4. Inconsistent extrusion from a slipping extruder or uneven filament.

Fixes

• Use a layer height that suits your Z axis. The Nozzle and Layer Height Picker helps choose sensible values for your nozzle, and the Steps per mm Calculator shows your Z steps per mm.
• Check the lead screw is straight and the coupler is not forcing it off-centre. Clean and lightly lubricate it.
• Make sure the bed uses PID temperature control, and run a PID tune.

Blobs and Zits

Symptom: small lumps on the surface, often lined up in a vertical seam or scattered where each layer starts and stops.

Causes, most likely first

1. Pressure in the nozzle at the start and end of each loop. Plastic keeps flowing for a moment after the extruder stops.
2. Seam position set to "nearest" or "random".
3. Retraction and wipe settings not tuned.
4. Wet filament popping in the nozzle.

Fixes

• Tune Linear Advance (Marlin) or Pressure Advance (Klipper) with the Linear / Pressure Advance calculator. This often makes the biggest difference to seams and corners.
• Set the seam to "aligned" or "rear", or hide it in a sharp corner.
• Fine-tune retraction, and try your slicer's wipe or coasting settings in small amounts.
• Dry the filament.

Clogs

Symptom: no plastic comes out, the extruder clicks or grinds, or extrusion gets weaker and then stops.

Causes, most likely first

1. Heat creep: heat travels up the heat break and softens filament where it should be solid. Common with PLA in a warm enclosure or when the hotend fan has failed.
2. A gap between the PTFE tube and the nozzle on many Bowden and some direct-drive hotends, where plastic pools and jams.
3. Debris or burnt plastic, including dust carried in on the filament.
4. Printing too cold, or retraction set very long.

Fixes

• Check the hotend (heat sink) fan runs all the time the hotend is hot.
• Do a "cold pull": heat up, push filament through, cool to below printing temperature, then pull the filament out firmly to bring debris with it. Repeat until the tip comes out clean.
• If the PTFE tube goes down to the nozzle, cut its end square and seat it hard against the nozzle.
• If all else fails, swap the nozzle. Always tighten a nozzle with the hotend hot, holding the heater block, as the hotend maker describes.
• For PLA in an enclosure, open the lid or door.

Ghosting and Ringing

Symptom: faint echoes or ripples on the surface just after sharp corners, letters or holes, fading with distance.

Causes, most likely first

1. High acceleration shaking the print head and frame at a resonant frequency.
2. Loose belts, wheels or frame bolts.
3. A heavy print head or a tall, wobbly printer on a soft surface.

Fixes

• Tighten belts, eccentric nuts and frame bolts. Put the printer on a solid surface.
• Reduce acceleration (and jerk or square corner velocity) and see if the ripples shrink.
• Use input shaping, which cancels the vibration so you can keep the speed. The Input Shaper Explainer takes Klipper calibration results and turns them into printer.cfg lines, a sensible max_accel, and Marlin M593 settings.

A Sensible Calibration Order

Calibrations affect each other, so doing them in order saves time. A common order is:

1. Mechanical checks: belts, wheels, frame, Z axis.
2. PID tune the hotend and bed.
3. Extruder e-steps (Steps per mm).
4. Bed level and first-layer Z offset.
5. Temperature tower for each new filament.
6. Flow rate (Flow Rate Calibration).
7. Pressure or Linear Advance (calculator).
8. Retraction (Retraction Settings).
9. Input shaping, if your firmware supports it (explainer).

Frequently Asked Questions

What is the most common cause of 3D printing problems?

The first layer. A wrong Z offset or a dirty bed causes poor adhesion, warping and elephant's foot, and can lead to layer shifts later. Wet filament is a close second, causing stringing, zits and rough surfaces.

How do I stop stringing in PETG?

Dry the filament first, then lower the temperature a little, tune retraction with a test tower and turn on combing or avoid crossing perimeters. A few fine wisps are normal with PETG and can be removed with a quick pass of a heat gun.

Should I calibrate e-steps or flow first?

E-steps first. E-steps make the extruder push the right length of filament; flow then fine-tunes for each filament's small differences. If you only adjust flow, you hide an extruder error that affects every filament.

Why are my layers shifting?

Usually because the nozzle hit a curled-up part of the print and the motor skipped steps, or because a belt or pulley is loose. Too much speed or acceleration can also cause it.

What causes regular lines on the sides of my print?

Z-banding. Check the lead screw and coupler, use a layer height that suits your Z axis, and make sure the bed heater uses PID control. If the spacing of the lines matches your lead screw pitch, the screw or its coupler is the likely cause.

Summary

Fix the basics first: dry filament, a good first layer, the right temperature, a clean nozzle and tight mechanics. Then match the symptom to its likeliest cause, change one setting at a time, and use the calibration tools in a sensible order. Most printers that "will not print" need only one or two of these fixes.