FDM Print Troubleshooter

Diagnose FDM print problems with guided checks for stringing, warping, bed adhesion, under-extrusion, layer shifts, and top-layer gaps.

10 symptoms · 6 with full guided trees · updated 2026-05

What is going wrong with your print?

Most likely causes — ranked

Based on your answers. Work top-down; fix one thing, re-print, re-check.

Stringing / oozing

Moisture in the filament Confidence: high

Fix

Dry the filament: PLA 45 C / PETG 65 C / ABS 70 C / Nylon 80 C for 4-6 h in a filament dryer or oven. Store with desiccant. Re-test before changing any slicer settings — wet filament masks all other tuning.
Stringing / oozing

Retraction disabled or far too short Confidence: high

Fix

Enable retraction. Start direct-drive 0.8 mm / Bowden 4 mm, retraction speed 35-45 mm/s, then run a retraction tower to dial it in.
Stringing / oozing

Nozzle temperature too high Confidence: high

Fix

Lower nozzle temp in 5 C steps (run a temp tower). Lower temp = more viscous melt = less ooze. Don't go so low you lose layer adhesion.
Stringing / oozing

Retraction needs tuning at this temp Confidence: medium

Fix

After lowering temp, re-run a retraction test; optimal retraction shifts with temperature.
Stringing / oozing

Travel speed too low Confidence: medium

Fix

Raise Travel speed to 150-250 mm/s (mechanically safe max). Less dwell time over the gap = shorter/no strings.
Stringing / oozing

Retraction slightly short Confidence: low

Fix

Add +0.5-1 mm retraction distance as a secondary measure.
Stringing / oozing

Travel path crosses open gaps unnecessarily Confidence: medium

Fix

Enable 'Avoid crossing perimeters' (PrusaSlicer/Orca) or set Combing Mode to 'Within Infill' (Cura). Hides residual stringing inside the part.
Stringing / oozing

No wipe / coast configured Confidence: low

Fix

Enable 'Wipe while retracting' and a small 'Extra restart distance' / coasting to relieve nozzle pressure before travel.
Stringing / oozing

Residual fine stringing after core tuning Confidence: medium

Fix

Fine-tune: small temp drop (-5 C), +0.3 mm retraction, enable wipe, and lower 'Z hop' if it dwells. Some materials (PETG) always string a little — a quick heat-gun pass cleans the part.
Stringing / oozing

Worn nozzle or partial blockage Confidence: low

Fix

If a known-good profile suddenly strings, inspect/replace the nozzle and do a cold pull.
Warping / curling

No enclosure / drafts on a high-shrinkage material Confidence: high

Fix

Enclose the printer (even a cardboard/acrylic box). Keep ambient warm and stable; eliminate drafts. This is the dominant fix for ABS/ASA warping.
Warping / curling

Part cooling fan too high Confidence: high

Fix

Set cooling fan to 0% for ABS/ASA (or <=20%). Rapid cooling drives differential shrinkage and warp.
Warping / curling

Bed temperature too low for the material Confidence: high

Fix

Raise bed temp: ABS/ASA 100-110 C, PC 110-120 C, PETG 70-85 C. Keep the first few layers hot.
Warping / curling

Weak first-layer grip lets corners peel Confidence: high

Fix

Degrease the plate with 90%+ IPA, lower Z offset slightly for a squished first layer, and slow first-layer speed to ~20 mm/s.
Warping / curling

Adhesive/surface mismatch Confidence: medium

Fix

Use the right adhesion promoter: glue stick or Magigoo for PETG/ABS on glass/PEI; ABS slurry for ABS. Smooth PEI can be too aggressive for PETG (use glue as a release + grip layer).
Warping / curling

Residual thermal stress on a large flat part Confidence: medium

Fix

Reduce infill % and add cooling-neutral design changes; large flat bottoms warp most. Consider splitting the part or printing at 45 deg.
Warping / curling

Drafts despite enclosure Confidence: low

Fix

Close the enclosure fully during the whole print; opening it mid-print to check causes a thermal shock that warps the next layers.
Warping / curling

Not enough anchored surface area at corners Confidence: high

Fix

Add a Brim (5-10 mm, e.g. 'Outer brim only'). For severe ABS warp use a raft or 'mouse ears'/brim discs at the corners.
Warping / curling

Sharp corners concentrate peel stress Confidence: medium

Fix

Add small fillets/chamfers to base corners in CAD; rounded corners warp far less than sharp ones.
Poor bed adhesion

Nozzle too far from the bed / bad Z-offset Confidence: high

Fix

Re-level (or run mesh bed leveling) and lower Live Z / Z-offset in 0.02-0.05 mm steps until lines fuse into a smooth sheet. Use a first-layer test print.
Poor bed adhesion

Grease/oil film on the build plate Confidence: high

Fix

Wash the plate with dish soap + water or wipe with 90%+ IPA. Handle by the edges only. For PEI, an occasional light scuff with a fine ScotchBrite restores tooth.
Poor bed adhesion

Bed temperature wrong for the material Confidence: high

Fix

Set bed temp to the material's range. If the first layer still won't stick at the right temp, add +5 C for the first few layers only.
Poor bed adhesion

First layer printed too fast Confidence: medium

Fix

Set first-layer speed to 20-25 mm/s and first-layer height to 0.2-0.3 mm. Slower, thicker first layers bond far better.
Poor bed adhesion

First-layer flow too low Confidence: medium

Fix

Increase 'First layer flow/extrusion' a few % so lines merge fully into the plate.
Poor bed adhesion

Insufficient bottom contact area for the geometry Confidence: medium

Fix

Add a Brim (skirt won't help) or raft for small-footprint / tall parts. Increase bottom layer count.
Poor bed adhesion

Warping pulling the part off mid-print Confidence: medium

Fix

If it sticks then detaches later, treat it as a warping problem: enclosure, lower cooling, higher bed temp, brim.
Poor bed adhesion

Drafts or AC blowing on the bed Confidence: low

Fix

Shield the printer from direct airflow; cold drafts on the plate kill first-layer adhesion.
Poor bed adhesion

Surface/material mismatch Confidence: medium

Fix

Use a glue-stick layer as both adhesive (PLA/ABS) and release agent (PETG on PEI). Smooth PEI for PETG should always have a glue barrier. Consider a dedicated sheet (textured PEI, garolite for nylon).
Under-extrusion

Partial nozzle clog Confidence: high

Fix

Cold/atomic pull, or replace the nozzle. Then do a flow test. A partly blocked nozzle is the most common constant under-extrusion.
Under-extrusion

Nozzle temperature too low for the flow Confidence: high

Fix

Raise nozzle temp 5-10 C (run a temp tower). Cold plastic can't be pushed fast enough and the filament strips.
Under-extrusion

Extruder tension / worn drive gear Confidence: medium

Fix

Set correct idler tension; clean filament dust from the drive gear; inspect for a worn/clogged gear.
Under-extrusion

Line width / layer height geometry Confidence: medium

Fix

Ensure layer height <= 75% of nozzle diameter and line width ~100-120% of nozzle. Too-thin layers or too-narrow lines look like under-extrusion.
Under-extrusion

Residual partial clog Confidence: low

Fix

If flow is calibrated yet walls are gappy, re-check the nozzle with a cold pull.
Under-extrusion

Flow rate / E-steps not calibrated Confidence: high

Fix

Calibrate E-steps (command 100 mm, adjust until exactly 100 mm feeds) then tune Flow/Extrusion multiplier with a single-wall or flow-calibration test.
Under-extrusion

Wrong filament diameter set Confidence: medium

Fix

Confirm filament diameter is 1.75 mm (not 2.85/3 mm) in Filament settings; a wrong value scales flow.
Under-extrusion

Exceeding hotend max volumetric flow Confidence: high

Fix

Lower print speed or set a 'Max volumetric speed' limit (run a flow-rate/max-flow test). Or fit a higher-flow hotend (e.g. CHT/high-flow nozzle) for big/fast prints.
Under-extrusion

Nozzle temp too low for the flow rate Confidence: high

Fix

Raise nozzle temp 5-15 C; higher flow needs more heat to keep the melt going.
Under-extrusion

Localized — heat creep or intermittent feed Confidence: medium

Fix

Check hotend fan is running full; on long Bowden setups reduce excessive retraction. Dry the filament (moisture causes intermittent thin spots).
Under-extrusion

Pressure/seam artifacts mistaken for under-extrusion Confidence: low

Fix

Tune Pressure Advance / Linear Advance so line starts aren't thin; gaps at perimeter starts are a pressure issue, not flow.
Layer shifting

Head collided with a raised blob or warped section Confidence: high

Fix

Fix the root defect first (warping/blobs), then enable Z-hop on retraction and 'Avoid crossing perimeters' so the head clears obstacles. Add a brim to stop corner lift.
Layer shifting

Speed/acceleration exceeds motor torque Confidence: high

Fix

Reduce print speed ~20% and lower acceleration/jerk in slicer or firmware. Bed-slingers: keep the moving-mass axis conservative.
Layer shifting

Loose belt or slipping pulley set screw Confidence: high

Fix

Tension belts until they twang; tighten pulley grub screws onto the motor-shaft flat. A pulley that slips on the shaft is a classic single-axis shift.
Layer shifting

Stepper driver overheating / current too low Confidence: medium

Fix

Add cooling to stepper drivers; raise driver current (Vref/TMC) slightly. A driver that thermally shuts down mid-print causes a shift then resumes.
Layer shifting

Motor or driver wiring fault Confidence: low

Fix

Check the motor connector is seated and the coil wiring is intact; an intermittent connection causes random shifts.
Layer shifting

Axis binding / debris / cable drag Confidence: high

Fix

Clean and lubricate rods/rails, check for a tight cable chain or wiring snag, ensure linear bearings/wheels are adjusted (V-wheels not over/under-tight).
Top-layer gaps / pillowing

Not enough top solid layers Confidence: high

Fix

Increase 'Top solid layers' to 5 (or set Top shell thickness ~0.8-1.0 mm). More layers progressively close the gaps over infill.
Top-layer gaps / pillowing

Infill too sparse to support the top Confidence: high

Fix

Raise infill to 15-20%+, or enable a denser 'Top/bottom-only' infill, or set 'Infill anchor' / 'Ensure vertical shell thickness'. A gyroid/grid at 20% supports tops well.
Top-layer gaps / pillowing

Insufficient cooling on bridged top layers Confidence: medium

Fix

Increase fan for bridges/top layers (PLA up to 100%; PETG 30-50%). For ABS you can't add much fan, so lean on more top layers + denser infill instead.
Top-layer gaps / pillowing

Top infill/ironing tuning Confidence: medium

Fix

Slightly increase top-layer flow (+3-5%), enable 'Monotonic' top surface (Orca/Prusa) and optionally 'Ironing' for a sealed finish.
Top-layer gaps / pillowing

Top pattern bridging poorly Confidence: low

Fix

Set top surface pattern to Monotonic/Rectilinear and reduce top-layer speed ~30% so it lays cleanly over infill.
Top-layer gaps / pillowing

Underlying under-extrusion shows worst on top Confidence: high

Fix

Fix flow first: calibrate Flow/E-steps, raise temp, clear any partial clog (see the Under-extrusion symptom). Then re-check the top.

Use the 2026 buying guide if the machine itself is the problem and the required part size or material exceeds its documented capabilities.

Tip: every symptom is deep-linkable — e.g. /troubleshoot/#warping jumps straight into that diagnostic. Educational guidance; always confirm with a calibration test.

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