Prusa 4 not printing
My Prusa 4 intermittant not printing since November of 2025.
Tried updating to 4s. Replaced Heatsink, Replaced Planetary Gears. Run all calibration tests with no faults. Checked MMU3, checked screws on extruder. Updated to newest firmware.
Load filament to printhead using control panels, works most of the time. When printing from Prusa Connect, filament loads to extruder sensor and no furthur. Tension screws are 35mm with small 5mm adapter as per original build instructions and tightened so end of screw level with front of idler-nut. Tried without adapter and adjusted other settings. Printer still not working. Fault seemed to coincide with update in November.
Tried reinstalling Firmware update
When printer does start to print on the rare occasion when changing colour, filament stops at extruder sensor and fails to print.
Going to reprint idler assembly on Extruder
or am I overlooking something
RE: Prusa 4 not printing
And do you even have a sensor installed in the MMU version on the Nextruder? And if so, do you have this option set in the printer menu?
RE: Prusa 4 not printing
Sensors set set in control panel for extruder and MMU.
Did a cold pull. Had to use a lot of force to get filament through the extruder lever even when screws loosened off. Replaced extruder lever and nut but still the same. Planetary gears (New) don't seen to grab filament. Filament stops advancing as soon as it hits the brass nut with blue collar on extruder. Once filament gets passed extruder lever, printer works ok.
changing colour works but filament stops when entering extruder
Just checked setting on MMU, everything seems ok
Printer was working OK for 2 years. It's got to be something obvious
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Going to try and print transucent gearbox cover to see if I can see where the problem lies
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I've managed to print x3 times in a row. First time for 4 month. I've replaced the main plate. The guide hole is slightly worn, elongated.
RE: Prusa 4 not printing
Thought I'd fixed problem with printing esp. more than one colour. I've replaced parts, calibrated multiple times as per manual. set the PTFE length between MMU3 and extruder. It doesn't just fail changing colour. When inserting filamant into extruder, the sensor advised filament detected, but the planetary gears haven't got hold of the filament, so printing nothing. I gradually increased the length of the PTFE tube in the hardware until filament caught by the planetary gears, but then I get failure premature filament detected.
Had no problems for over 18 months. All seems to tie in with Firmare update in November 2025, tried old Firmware to no avail
Cleaned and adjusted MMU3, Clead and adjusted Extruder etc
Replaced :- planetary gears and washer, heatsink with new sensor, extruder lever and nut, nozzle, Main Plate, upgraded fro Prusa 4 to Prusa 4S, updated firmware on main board and MMU3.
Can't print multiple colours until problem fixed, Im wasting reels of filament