The CORE One is Prusa’s first CoreXY machine, and it inherited most of its error-reporting system from the MK4S and XL rather than inventing a new one. When something trips a fault, the printer’s screen shows a short error name, a plain-language description, and a five-digit code alongside a QR code you can scan with a phone. That QR code lands on a matching page at help.prusa3d.com, which is also where the information in this article comes from. Because Prusa reuses one error database across its whole current lineup (CORE One, CORE One L, MK4S, MK3.9, MK3.5, XL, MINI), each article on the knowledge base lists several codes side by side, one per printer model. On the CORE One and CORE One+, the code always starts with 31; the CORE One L uses 35, and the newer CORE One INDX uses 36.
The numbering isn’t officially documented as a formal schema the way Bambu Lab’s HMS codes are, but a pattern is visible once you look at enough of them. Codes in the 311xx range tend to cover sensors and mechanical checks (filament detection, door sensor, bed evenness). The 312xx range is almost entirely temperature-related. 313xx covers motion, homing, and low-level electrical faults. 315xx is the loadcell, ESP32 Wi-Fi module, and general firmware/memory bucket. 316xx is firmware and USB flashing. 317xx covers firmware update prompts. And 318xx is the largest group by far, covering everything that can interrupt an active print, from crash recovery to fan faults to MMU handling. Treat that grouping as an observation, not a spec Prusa has published.
Because the CORE One is a closed, actively-heated CoreXY enclosure with a chamber thermistor, a loadcell-based nozzle-to-bed probing system (no physical limit switch on Z), a MODBUS-driven “puppy” architecture for its extension boards, and two filament sensors instead of one, several of its errors don’t exist on Prusa’s older open-frame printers at all. Those are the ones worth knowing before you own the machine.
Selftest and first-boot calibration
The first thing most new CORE One owners run into isn’t an error code so much as a failed step in the Selftest, which is part of the Calibration Wizard that runs automatically on first boot or after a factory reset. It checks, in order: the hotend, print, and chamber fans; the door sensor; X and Y axis movement; Z alignment; the loadcell; the heaters; and the filament sensors.
A failed fan test usually means a connector isn’t seated on the LoveBoard or xBuddy extension board, or the hotend fan is mounted in the wrong orientation. A failed X or Y axis test is almost always belt tension or gantry skew; Prusa’s own fix involves loosening the belts completely, squaring the gantry by hand against the front rail, and retensioning. A failed Z alignment step points to the trapezoidal nuts on the three Z motor threaded rods binding or spinning roughly, which a look through the official assembly guide’s video is the fastest way to diagnose. A failed loadcell test is frequently caused by the printer sitting on an unstable surface, since any vibration reaching the frame gets read as a false force reading. None of these produce a numbered QR code on their own; they only show a pass/fail checkmark on the selftest summary screen. If the failure is later reproduced as a live error during printing, that error will have its own code and its own QR link.
Beyond the selftest, two codes cover ongoing calibration state: Homing calibration needed #31118 and Calibrate homing from menu #31120, which appear when the printer wants you to redo the axis homing routine, and Loading obstruction #31119, which fires when something is blocking the filament path during a load attempt.
Enclosure and chamber errors
This category is new territory for Prusa and specific to the CORE One’s closed-chamber design. Door Open #31110 shows “Close the door to prevent air drafts, burns, and other undesirable effects” if you try to start a print with the door open; the door sensor can be disabled from Settings -> Hardware -> Door Sensor if you genuinely want to print open, though Prusa’s own documentation notes that with the active fans, you don’t need the door open even for PLA.
Chamber temperature has its own family of codes: Chamber MAXTEMP error #31214 and Chamber Mintemp error #31215 cover the chamber thermistor reading out of range, Chamber overheating #31260 and Chamber temperature is critical #31261 are progressive warnings as the enclosure gets hotter than intended, and Failed to Reach Chamber Temperature #31259 appears when active-chamber-heating materials like ABS or ASA can’t get the enclosure up to the target temperature in time. There are also two housekeeping prompts, Open chamber ventilation #31837 and Close chamber ventilation #31838, tied to the motorized vent that’s part of the CORE One’s active chamber management, plus Chamber filtration fan is not spinning #31840 and Chamber Cooling Fan Error #31839 for the fans that handle particulate filtration and cooldown. Uneven bed #31111 and Ceiling clearance violation #31112 are two more CORE One-specific safety checks: the first flags a bed that isn’t level within tolerance during probing, the second flags a print tall enough to risk hitting the underside of the enclosure lid or gantry.
Temperature and heating
This is the largest inherited category and covers the hotend, heatbed, and heatbreak independently. Bed preheat error #31201 and Hotend preheat error #31202 mean a heater isn’t reaching temperature in the expected time, usually a wiring or thermistor fault. Bed thermal runaway #31203 and Hotend thermal runaway #31204 are safety cutoffs that fire when a heater’s temperature reading disagrees badly with what the firmware commanded, which almost always means a damaged thermistor, a loose connector, or in rare cases a stuck heating element. Bed mintemp #31207 / maxtemp #31205 and Hotend mintemp #31208 / maxtemp #31206 cover readings outside the sane range in either direction, which is again usually a thermistor or cable problem rather than the heater itself. The heatbreak, the metal section between the hotend’s heated block and the cold zone, has its own pair: Heatbreak MINTEMP Error #31211 and Heatbreak MAXTEMP Error #31212. Heatbed temp not matching #31209 and Hotend temp not matching #31210 flag a discrepancy between two independent temperature readings for the same component, which is a sanity check Prusa added specifically to catch a failing thermistor before it triggers a full runaway.
Motion, homing, and crashes
Homing error Z #31301 covers a failed Z-axis home, which on the CORE One usually traces back to one of the three Z motors’ trapezoidal nuts binding on the threaded rod, the same issue that shows up during the selftest. Homing error articles exist for X and Y as well, shared with the XL. Power Panic #31321 appears when the printer detects damage to the power panic cable, the wire that runs from the PSU to the xBuddy board and lets the firmware save state and resume a print after a sudden power loss; Prusa notes there are two compatible cable variants (single-wire and two-wire) on CORE One, MK4/S, and MK3.9/S, and mixing electronics revisions without the matching cable is a documented cause of false Power Panic triggers.
Crash recovery, the system that lets the printer re-home and resume after a layer shift or physical knock, has its own small cluster: Crash recovery axis long #31809, axis short #31810, home fail #31812, and repeated crash #31811, the last of which appears when the printer keeps detecting crashes on the same axis and gives up rather than looping indefinitely. Accelerometer communication failed #31323 covers the input-shaper accelerometer losing contact with the mainboard, which will also block resonance calibration until it’s resolved.
Filament handling and the Nextruder
The CORE One carries over the Nextruder toolhead from the MK4S but keeps a second filament sensor near the PTFE tube inlet on the side panel, so both sensors have to agree for reliable retraction timing. Stuck filament detection #31101 fires when the extruder gears are turning but the filament sensor isn’t seeing movement, which usually means a clog, a grinding gear, or filament tangled on the spool. Filament sensor stuck #31113 and Filament Sensors Disabled #31115 cover the sensors themselves misbehaving or being manually turned off, and there’s a dedicated Fil. sensor troubleshooting #31114 article that walks through cable and lever checks for the side sensor specifically. Extruder not detected #31615 points to a communication fault with the Nextruder’s onboard electronics rather than the filament path. During print start, Filament not detected #31804 and Print preview wrong filament #31805 are both sanity checks comparing what’s loaded against what the sliced file expects.
Electronics, firmware, and communication
The CORE One’s extension boards (what Prusa’s firmware calls “puppies”) talk to the xBuddy mainboard over MODBUS, and a large block of codes, Puppy error #31511 through #31522, covers failures in that link, from address assignment problems to lost communication with a specific board. The I2C Send/Receive family (#31311 through #31318) covers a separate internal bus used for EEPROM and sensor communication, and the ESP Error codes (#31504, #31505, #31506) and ESP not connected #31533 cover the Wi-Fi module used for Prusa Connect. Loadcell Not Calibrated #31523, Tare Error #31524, Tare Failed #31525, Measure Failed #31526, Bad Configuration #31527, and Timeout #31528 are all failure modes of the same strain-gauge sensor the selftest checks, since it’s also used live during every print to detect the first-layer contact instead of a physical Z-endstop switch.
On the firmware side, Unknown error #31601 is a catch-all: it means the printer hit a fault that isn’t in Prusa’s own error database yet, and the fix is to make sure firmware is current, reproduce the issue if possible, save the log, and contact support or file it on Prusa’s GitHub. Blue Screen of Death #31538, called BSOD even though firmware 6.5.1 and later actually shows a black screen, is a hard internal fault outside the normal red-screen error system; Prusa’s advice is to try a different USB drive if it happened during file selection, power-cycle if it happened over Connect, and save the crash dump from Settings -> System -> Save Crash Dump if support asks for it. Firmware x printer mismatch #31609, Signature verification failed #31606, and Hash verification failed #31607 all relate to the firmware update and secure-boot chain rejecting a file that doesn’t match the expected printer type or checksum.
Print-in-progress messages and warnings
Not every code in this list is a hard failure. New firmware available #31802, Print preview unfinished selftest #31801, Maintenance warning #31117, and Maintenance failure warning #31116 are informational prompts. Quick pause #31835 and G-code cropped #31535 / G-code corruption #31534 sit in between: the first is a deliberate user-triggered pause, the other two flag a sliced file that got truncated or corrupted in transfer, usually from an interrupted USB copy or a flaky network transfer to Connect. Heaters Timeout #31817, Nozzle Timeout #31819, and Steppers timeout #31820 all cover the firmware giving up on a component that didn’t respond within its expected window, generally pointing at a wiring or board fault rather than a settings issue.
The CORE One inherited most of its error database from Prusa’s Buddy-board lineage. See the Prusa MK4 Error Code Index for the same error names under different five-digit codes, since the CORE One’s CoreXY hardware shifts several fault numbers even when the underlying part (thermal runaway, homing, loadcell) is the same.
Errors tied to routine service, like the periodic maintenance reminders, are covered in the CORE One maintenance schedule, while a persistent Nozzle Timeout or heating fault is often resolved by working through the nozzle replacement guide rather than repeating the self-test alone. The Einsy-based Prusa MK3S+ predates this QR code system entirely and shows plain-text messages like MINTEMP or Bed leveling failed instead.
The CORE One shares its five-digit QR error architecture with the rest of the current Prusa lineup, including the multi-toolhead XL. See the Prusa XL Error Code Index for the tool-changer and modular-bed codes that are unique to that larger printer.