Printer model
Original Prusa MK4S: nozzles, power supply and upgrade kits
Prusa's MK4S specs: Prusa Nozzle CHT, 290 °C, 240 W Delta PSU, maintenance intervals, the MK4 to MK4S kit, and the PSU that does not fit it.
Also listed as MK4, MK3.9
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Short answer
Prusa lists the MK4S with a 250 x 210 x 220 mm build volume, a 0.4 mm brass CHT Prusa Nozzle, a 290 °C nozzle maximum and a Nextruder with a 10:1 planetary gearbox. Its power supply is a 240 W Delta unit with Power Panic. Prusa's separate PSU 24V 240W assembly is for the MK3/S/+ only and does not fit the MK4, XL or CORE One.
What fitsAll 2 items that fit
- Diamond-tip spare nozzleDiamondBack Prusa Nextruder nozzle, 0.4 mm (polycrystalline diamond tip)Check price on Amazon
Key facts
- Build volume
- 250 x 210 x 220 mm[1]
- Motion system
- Not confirmed
- Stock extruder
- Nextruder with a 10:1 planetary gearbox[1]
- Stock hotend
- Not confirmed
- Nozzle standard
- Prusa Nozzle (Nextruder); E3D V6 nozzles only with the Nextruder V6 Nozzle Adapter[2][1]Prusa does not confirm that MK8 nozzles work with the adapter.
- Stock nozzle
- 0.4 mm brass CHT high-flow Prusa Nozzle[1]
- Max nozzle temperature
- 290 °C[1]
- Max bed temperature
- Not confirmed
- Firmware
- Prusa firmware, flashed from a USB drive with the package for the specific printer model[3]Prusa says to use the USB method even when Prusa Connect offers the update.
- Latest listed firmware
- Not confirmedPrusa added input shaper to the MK4 with firmware 5.0.0; we did not record the current MK4S version.
- Power input
- 240 W power supply made by Delta, with Power Panic hardware[4][5]Prusa's PSU 24V 240W assembly is compatible only with the MK3/S/+, not with the MK4, XL or CORE One. The MK4S page states no input voltage range or bed voltage.
- Hardware revisions
- Newer and older xLCD units: the MK4 to MK4S kit comes in separate options, so check your xLCD version before ordering[6]
- Maker maintenance rules
- Sporadic checks every 200 printing hours; electrical connector checks every 600-800 hours; no lubricant on the Z-axis trapezoid nuts or threaded lead screws[7]Prusa's guide covers the MK4, MK4S, MK3.9 and MK3.9S. It says the Nextruder primary gear and idler-shaft bearings need no lubricant.
- Documented upgrade kits
- Prusa MK4 to MK4S kit (adds a 360° cooling fan with shroud and a brass 0.4 mm CHT nozzle); Prusa MK3/S/+ to MK4S kit[6][8][9]See the Original Prusa MK3S+ record for what the MK3 kit reuses and its prerequisites.
- Recall status
- No recall found on 2026-10-08[10]On 2026-10-08 we found the Bambu Lab A1 recall as the only 3D printer recall in CPSC's notices. That is a dated search, not proof that no recall exists.
- Not confirmed
- Not confirmedThe MK4S pages we read state neither the input range nor the bed voltage.
Watch out for
- Prusa's PSU 24V 240W assembly fits the MK3/S/+ only. Prusa says it is not compatible with the MK4, XL or CORE One, whatever a reseller listing says.
- V6 nozzles fit a Nextruder only with Prusa's Nextruder V6 Nozzle Adapter. Prusa does not confirm MK8 nozzles with it.
- Prusa's MK3S+ nozzle procedure (280 °C, 2.5 N·m) is for V6 printers. Do not apply it to a Nextruder.
- Prusa stops heating and shows a hotend thermal runaway error if the nozzle drops by 12 °C and does not recover within 60 seconds. Error codes differ per model, for example #13204 on the MK4 and #26204 on the MK4S.
- Prusa says its Accelerometer Set is not needed on a stock printer, because factory input-shaper values are pre-tuned.
What fits
Product details below are the seller's own description unless a source is shown. Pick the variant named for each item.
Spare nozzle
E3D brass Prusa Nextruder nozzle, 0.4 mm (PRUSA‑MK4‑NOZZLE‑AS‑0400)Choose the 0.4 mm brass Prusa Nextruder nozzle (PRUSA-MK4-NOZZLE-AS-0400), not a V6 nozzle.
E3D lists its Nextruder nozzles for the MK4S, MK4, MK3.9, XL and CORE One. Brass is not for abrasive filaments.
Diamond-tip spare nozzle
DiamondBack Prusa Nextruder nozzle, 0.4 mm (polycrystalline diamond tip)Choose the 0.4 mm DiamondBack Prusa Nextruder nozzle, not a V6 nozzle.
Prusa lists it for the MK4S, rates it to 300 °C and says it is not high flow. A premium nozzle for abrasive filaments.
Prusa says the Original Prusa MK4S was the first consumer 3D printer to receive UL GREENGUARD Certification. That is Prusa's claim; we did not check it in UL's database. GREENGUARD concerns emissions, not electrical safety.
Aliases: the MK4 and MK3.9 share the Prusa Nozzle, the USB firmware method, the maintenance guide and the thermal runaway rule above. The build volume, nozzle, temperature and power supply figures are Prusa's MK4S figures.
Questions
Does Prusa's PSU 24V 240W fit the MK4 or MK4S?
No. Prusa lists that PSU assembly as compatible only with the MK3/S/+ and not with the MK4, XL or CORE One. The MK4S uses a 240 W Delta unit with Power Panic.[5][4]
Can I use V6 nozzles on an MK4S?
Only with Prusa's Nextruder V6 Nozzle Adapter. The MK4S ships with a 0.4 mm brass CHT Prusa Nozzle.[2][1]
What do I check before ordering the MK4 to MK4S kit?
Prusa says to check your xLCD version first, because the kit has separate options for newer and older xLCD units. See MK3S+ and MK4 to MK4S upgrades.[6]
Should I grease the MK4S lead screws?
No. Prusa says not to apply lubricant to the Z-axis trapezoid nuts or threaded lead screws on the MK4/S and MK3.9/S; Prusa Lubricant is for the smooth rods and linear bearings.[7]