My Prusa Core One started having problems during prints, and I can’t figure out what changed. It was working fine before, but now I’m getting failed prints and inconsistent results. I need help troubleshooting the cause so I can get it printing normally again.
Start with the boring stuff. Most print failures come from 5 areas.
-
Filament
Dry it. Especially PLA if it sat out. Wet filament gives random blobs, weak layers, stringing, and ugly top surfaces. Try a fresh spool first. Easy test. -
Nozzle and hotend
Swap in a new nozzle or do a cold pull. Partial clogs cause under-extrusion and inconsitent walls. Check if the sock is torn or hanging loose too. -
First layer and bed
Wash the sheet with dish soap and hot water. Re-run first layer calibration. Check bed mesh. If one side starts failing, look for debris under the sheet or a warped plate. -
Belts and motion
Check belt tension on X and Y. Loose belts give shifted layers and ringing. Too tight gives rough motion. Move the toolhead by hand with power off. It should feel smooth, not grindy. -
Slicer and settings
If it worked before, load an older gcode or old profile and print the same part. If old gcode fails too, it is hardware. If old gcode works, you changed a setting. Common ones are temp, retraction, speed, volumetric flow.
Also check:
Firmware update?
Extruder gear packed with dust?
Part cooling fan spinning normal?
PINDA or probe mount loose?
Z offset changed a tiny bit?
Post photos of the failed print, filament type, nozzle size, temps, and what failed changed from before. That narrows it down fast.
I’d add a couple things beyond what @andarilhonoturno listed, because “it was fine and now it isn’t” is often a clue that something drifted, not fully failed.
First, check the spool path from holder to extruder. I’ve seen weird intermittent under-extrusion that had nothing to do with the nozzle at all, just the filament catching on the spool edge or feeding with too much drag. Same idea with a PTFE guide if you’re using one. Tiny resistance, big print weirdness.
Second, inspect the idler pressure on the extruder. Too loose and it slips sometimes, too tight and it chews filament and makes dust. Those failures can look super random. If you see ground-up filament near the drive gears, that’s a big hint.
Third, pay attention to heat creep, especially if failures start mid-print instead of right away. If the hotend fan is spinning but weak, noisy, or pulsing, that can soften filament too high up and cause jams that come and go. People check the part cooling fan a lot, but the hotend fan is the sneaky one.
I’d also not assume wet PLA is the first suspect every time. It can matter, sure, but sudden failures after a machine was printing fine often point more toward mechanical drift, fan issues, or a developing clog than “the PLA got sad.”
Best diagnostic print is not a full model. Print:
- a 20mm cube
- a single-wall vase cube
- a first-layer test
- then the exact old file that used to work
That combo tells you way more, way faster. If you can post pics of the failure pattern, people can usually tell in like 30 sec what family of problem it is.
I’d go one layer deeper than @andarilhonoturno and look at the “stuff around the print,” not just the filament path.
Big one on Core One: environment changes. If the printer got moved, enclosed differently, or sits near a vent/window now, chamber temp can shift enough to mess with layer adhesion, warping, and even extrusion consistency. Sudden problems sometimes come from the room, not the machine.
Also check motion system health:
- belt tension left vs right
- pulley grub screws
- any play in toolhead or bed movement
- rods/rails needing cleaning
A slightly loose pulley can fake a slicer or extrusion issue because the artifact shows up as random layer shifts or ringing.
I’d also verify slicer profile drift. Sometimes a profile gets edited, nozzle diameter changes in settings, pressure advance values get tweaked, or volumetric speed gets pushed too high. If an old file fails now, print it from the exact same old gcode if you still have it. If old gcode works but newly sliced files fail, that points away from hardware.
One place I slightly disagree with the usual advice: I would not start with a nozzle swap unless you already see clear clog symptoms. Swapping parts too early muddies the diagnosis.
For the ‘’:
- Pros: simple, readable, easy to compare test results
- Cons: not useful unless you log changes one at a time
What would help most is photos of the failed layers plus whether it fails at start, mid-print, or near the top.
Try a zero variables baseline.
- Factory reset the printer.
- Load the stock Prusa Core One profile in PrusaSlicer 2.x.
- Use a fresh Prusament PLA spool, dry 4 hours at 45 C.
- Rerun frist layer cal and PID tune for hotend and bed.
- Print the bundled 20 mm cube gcode from the SD card.
- If it passes, slice the same cube with the stock profile and print.
- If it fails on the bundled gcode, stop. Fix hardware next.
This takes 60 to 90 mins and isolates software, filament, and thermal control fast.