The Prusa MINI+ runs Prusa’s in-house firmware on a Buddy mainboard, the same firmware family used across the CORE One, MK4S, and XL lines, but with its own set of printer-specific safety checks and error codes. When something goes wrong, the MINI+ shows a red error screen with a short description and, on most firmware versions, a QR code you can scan with a phone to jump straight to the relevant help article. Each error also has a numeric code in the pattern XXYZZ: the first two digits identify the printer (12 for the MINI), the next digit marks the error category (for example, 2 for temperature faults), and the last two digits identify the specific fault. You can look any code up directly at help.prusa3d.com/en/{code}, and the printer’s Settings menu lets you turn the embedded device hash in the QR code on or off, which only affects diagnostic reporting, not the error itself. Below is a rundown of the fault types Prusa documents for the MINI+, grouped by what part of the printer they relate to. The MINI+ does not support Prusa’s MMU filament-changer add-on the way the MK3S+, MK4, and XL do, so there are no MMU-related fault codes for this model.
Thermal and heating faults
Most of the MINI+’s heating errors come in matched pairs, one for the heatbed and one for the hotend, and they all trip a safety cutoff that kills the heater and freezes the print rather than letting a runaway heater keep going. A Preheat error appears when a heater cannot bring the target component up to temperature fast enough during initial heating: for the heatbed (#12201) the trigger is less than 2°C of rise in 240 seconds, and for the hotend (#12202) it’s less than 2°C of rise in 20 seconds. A Thermal runaway error fires mid-print if a heater that was already at temperature suddenly loses heat and doesn’t recover: the bed version (#12203) triggers on a 25°C drop that isn’t recovered within 45 seconds, and the hotend version (#12204) triggers on a smaller 6°C drop not recovered within 20 seconds, reflecting how much faster the hotend cools relative to the bed. In both cases, Prusa’s documented fix is the same: check the heater and thermistor wiring for damage or a loose connector at the Buddy board, then measure resistance directly, expecting roughly 80-125 kΩ for a thermistor and single-digit ohms for the heater itself (the exact heater range differs slightly between bed and hotend). A Maxtemp error (#12206 for the hotend, documented as triggering above 305°C; #12205 for the bed) means a component read an unsafe high temperature, while a Mintemp error (#12207 for the bed, triggering below 15°C at any point; #12208 for the hotend) usually points to a disconnected or failed thermistor rather than an actually cold part. There are also “Temp not matching” errors (#12209 for the bed, #12210 for the hotend), which happen when the measured temperature sits close to but not exactly at the target, a pattern Prusa attributes to a thermistor that has partially failed or lost solid contact with the heater block or bed. Separately, a Heaters Timeout message (#12817) isn’t a fault at all: it’s the printer automatically switching off heating after 30 minutes of idling with no print running, and clearing it just means reheating manually from the LCD menu if you need to.
Homing and motion faults
Before any print, the MINI+ has to find its physical home position, and if it can’t, it throws a homing-related error rather than risk crashing into the frame. The generic Homing Error (#12301) is specific to the Z axis: the firmware takes two separate readings from the MINDA or SuperPINDA probe as it approaches the steel sheet, and if those two readings disagree by more than 0.1 mm, homing fails. Prusa’s fix path starts with testing the probe itself, then checking that the Z axis moves freely by hand with the printer off, looking specifically at whether the trapezoidal nut and both Z-carriage parts are seated evenly. Homing error X (#12304) and Homing error Y (#12305) are separate codes for the two horizontal axes, and both point to the same family of causes: something physically blocking the axis (often a stray bit of filament wrapped around a smooth rod or belt), incorrect belt tension, or a motor pulley whose set screws aren’t seated against the flat part of the motor shaft, which lets the pulley slip on the shaft without actually moving the axis. A separate Emergency stop message (#12510) shows up when the printer receives an M112 G-code command, most often during serial printing over something like OctoPrint, and Prusa’s own guidance here is limited: disconnect any external control software, reboot, and try printing from a USB drive instead to see if the same fault recurs.
Filament sensor and mechanical faults
The MINI+ can be ordered with, or have added later, an optional IR filament sensor that uses a mechanical lever and the same sensor electronics as the MK2.5S and MK3S+ filament sensors. It isn’t a standard part of every MINI+ build, so if you don’t have one installed, none of this applies to your printer. When it is installed, its live status is readable from LCD menu -> Info -> Sensor info, showing 1 for filament present, 0 for no filament, or N/A if the sensor isn’t detected at all. Prusa’s troubleshooting distinguishes between a mechanically stuck lever, which you can test by moving it by hand, and a genuinely faulty sensor, which reports the same value (always 0 or always 1) regardless of the lever’s actual position. Beyond the sensor itself, the MINI+ documentation also covers filament that fails to unload cleanly, usually because the hot tip of the filament formed an irregular blob too wide for the PTFE tube; this isn’t a numbered error code, just a jam that Prusa walks through clearing by loosening the relevant brass fitting and pulling the stuck filament out with pliers. Note that a few other issues filed under “Troubleshooting” on Prusa’s site, like the so-called spaghetti monster (a failed print that detached from the bed mid-print), are print-quality problems rather than error screens, and the MINI+ doesn’t display a code for them.
Firmware, USB, and communication faults
A large block of MINI+ error codes, from #12602 through #12614, covers problems with the “Alternative Method” of flashing firmware from a USB drive, triggered by holding the reset button and pressing the LCD knob during boot. These include USB not connected (#12602), invalid firmware file size (#12603), no firmware file found on the drive (#12604), a flash erase error (#12605), signature verification failure (#12606), hash verification failure (#12607), firmware in the internal flash reported as corrupted (#12608), unsupported printer type (#12610), unsupported printer firmware version (#12611), no firmware present in internal flash (#12612), a file system error (#12613), and an unsupported BBF file version (#12614). Prusa’s fix across nearly all of these is the same short checklist: re-copy the firmware files fresh to a FAT32 USB drive, properly unmount it before removing it from the computer, and retry the flash procedure, trying a different USB stick if the problem persists. A Connect Registration Failed error (#12401) appears specifically when linking the printer to Prusa Connect fails, with the printer showing extra detail text after the main message. Finally, there’s a rarer catch-all: a Blue Screen of Death, called a Black Screen of Death from firmware 6.5.1 onward, carries its own internal error code (#12538 on the MINI) and covers crashes Prusa hasn’t mapped to a specific red QR-code error. Prusa’s own advice for a BSOD is mostly to power-cycle the printer and, if it keeps happening, save a crash dump from Settings -> System and send it to their support team directly, since there’s no generic self-repair path documented for this one.
The MINI+ uses the same Buddy-board error framework as Prusa’s other current printers, just without MMU support. See the Prusa MK3S+ Error Message Index and the Prusa MK4 Error Code Index for how the same fault categories play out on printers that do support the MMU.