Print problems after changing the nozzle: what to check

This guide is for anyone whose prints changed after fitting a new nozzle or hotend, whether it's the same size, a new diameter, or a hardened or high-flow version. It covers the printer and slicer settings each maker documents, the calibrations to repeat, the tightening steps for the hotends named in each source, and layer height for the new size. Steps are kept to the printer models each source names.

Step 1: Tell the printer which nozzle you fitted

Bambu Lab and Prusa both document a nozzle setting on the printer itself, and sometimes a nozzle type setting too. Set it before your first print with the new nozzle.

Bambu Lab X1, P1 and A1 series

Bambu's hotend guides for the X1 and P1 series and for the A1 series both say: "If you have replaced the nozzle with one of a different specification, please make sure that the nozzle information is manually updated on the screen before printing." On the A1 series, Bambu gives the path: tap Settings → Maintenance → Nozzle on the control panel.

You can't do this from the slicer any more. Bambu says that in Bambu Studio V02.01.01.52 or later, the nozzle information under "Printer Parts" is "now for display purposes only," and that "nozzle changes must be performed directly on the printer."

Prusa MK4S and MK3.9S

Prusa's nozzle replacement guide for these printers includes a Nozzle Setup step after the hotend is refitted. Go to Settings → Hardware → Printhead and set the Nozzle Diameter you're using. Prusa says to set the Hardened steel option to ON if you fitted a hardened steel nozzle, and to turn on Nozzle High-flow and Silicone Sock if you've installed those parts. For the MK4S and MK3.9S with the MMU3-modified extruder, it says to set the Nextruder option to [MMU].

Other Prusa printers

• Nextruder printers (CORE One, XL, MK4/S, MK3.9/S). Prusa's nozzle types article says to set a different nozzle size under Menu → Settings → Hardware.
• MINI/MINI+. Prusa's E3D V6 nozzle article gives the same path: Menu → Settings → Hardware.
• MK2.5/S and MK3/S/+. From firmware 3.13.0, Prusa says the nozzle size can be set under Settings → HW setup → Nozzle d., with options of 0.25, 0.40, 0.60 and 0.80. The 0.4 mm nozzle is the default.

On the MK3/S/+, Prusa says that if you set up a profile for a custom nozzle size, change Settings → HW setup → Checks → Nozzle to Warn, so you get a warning you can skip, or to None, so the printer ignores the difference.

Creality

Creality's K1 and K1C nozzle replacement pages include a check, not a settings change. After tightening, load the filament, lock the extruder clamp and operate the feeder to "check if the filament extrusion is normal." We didn't find a Creality wiki page that documents a printer-side nozzle size setting for these models.

Step 2: Match the slicer profile to the nozzle

Bambu Studio

Bambu says the printer preset "contains all of the printer hardware settings," including "the nozzle's diameter," and that "before slicing, you need to select the correct printer preset according to your machine." Its own example of a preset name is "Bambu Lab X1 0.4 nozzle." After a diameter change, slice with the preset for the new size.

PrusaSlicer

Prusa says to go to Menu → Configuration → Configuration Wizard → Prusa Research and select your printer model and the nozzle diameter you're using. It suggests unchecking the other models and diameters "to avoid confusing the presets." Except for the stock 0.4 mm presets, Prusa says each profile has the diameter in its name. If a profile doesn't say "0.25 nozzle," "0.6 nozzle" or "0.8 nozzle," it's for a 0.4 mm nozzle.

For a size without a built-in profile, Prusa says to change two things: the nozzle diameter under the Printers tab → Extruder 1, and the extrusion width under the Print settings tab → Advanced. It adds that changing the nozzle diameter "won't make PrusaSlicer generate thicker extrusion lines" on its own. Prusa also says PrusaSlicer writes the nozzle diameter into the G-code, so "the printer can warn you if you accidentally try to print a G-code generated for a different nozzle size."

High-flow and standard nozzles (Prusa CORE One, CORE One L, XL, MK4/S, MK3.9/S)

Prusa's clogged nozzle article for these printers says: "If your printer is equipped with a High Flow (HF) nozzle, you must use an HF print profile." It warns that using a standard profile for an HF nozzle, or the other way round, "throws off the volumetric flow calculations, which can lead to severe under-extrusion or structural clogs." If extrusion fell off after fitting an HF nozzle, check this before you take anything apart. For more on weak extrusion, see our under-extrusion guide.

Step 3: Rerun the calibrations your maker lists

Prusa MK2.5/S, MK3/S/+, MK3.5/S and MINI: First Layer Calibration

Prusa's nozzle change guides for the MK2.5/S, MK3/S/+ and MK3.5/S and for the MINI/MINI+ both say it's "necessary to redo the First Layer Calibration" after replacing the nozzle. For nozzles other than 0.4 mm, Prusa's E3D V6 nozzle article says to reset Live Adjust Z to zero first:

• MK3S+, MK3S and MK2.5S. LCD menu → Settings → Live Adjust Z.
• MINI. LCD menu → Calibration → Live Adjust Z.

Then print a single-layer box, which Prusa says you can make in PrusaSlicer by right-clicking an empty build plate, choosing Add Shape → Box, and scaling it 0.2 to 0.4 mm tall, depending on the nozzle. Adjust Live Z while it prints until the line is "flattened, but not squished," with no gaps or ridges between lines. Our first-layer lines guide shows how to read the result.

For small nozzles (around 0.25 mm), the same article says "calibration and bed leveling become even more important" and that "after changing the nozzle, make sure you at least run the Z calibration of your printer before you start printing." Prusa says that besides the First Layer Calibration, no further calibration is needed on the MINI.

Prusa MK4/S, MK3.9/S and XL

Prusa says the First Layer Calibration "is not required" on these printers. On the MK4 and XL, which have a load cell, it says any Live Adjust Z value is reset automatically after the next print.

Bambu Lab: Flow Dynamics Calibration

Bambu lists the cases where you need to run Flow Dynamics Calibration, including "when you replace the nozzle, due to manufacturing tolerances" and when the nozzle is worn out. In Bambu Studio, open Calibration → Flow Dynamics. During manual calibration, Bambu says to sync the printer's information and select the nozzle diameter installed on the printer.

Bambu also says a third-party hotend can make results unreliable, "especially relevant for the A1 series and H2D printers," where calibration uses an eddy current sensor. If the corners of your prints changed after the swap, our bulging corners guide covers the test patterns.

Step 4: Check the nozzle was tightened or seated correctly

Prusa warns that skipping steps in its MK2.5/S, MK3/S/+ and MK3.5/S nozzle procedure "can cause leaking and extrusion issues." Use the procedure for your exact hotend. The temperatures and torques below apply only to the hardware each source names.

E3D warns that applying too much pressure risks "shearing either the nozzle or HeatBreak." On the MK2.5/S, MK3/S/+, MK3.5/S and MINI, Prusa says there must always be a gap of about 0.5 mm between the nozzle and the heater block. For the MK2.5/S, MK3/S/+ and MK3.5/S, it says failing to lock the nozzle against the heat break "will cause leaks"; for the MINI, it says no visible gap can mean the nozzle didn't reach the heat break, "which can lead to leaks and clogs." On the MK4S and MK3.9S, the Prusa Nozzle is different: Prusa says to screw it in "until the nozzle touches the heaterblock surface," then tighten it without extra force.

For the two Micro Swiss hotends:

• FlowTech (K1 series). Micro Swiss says "there is no need to heat the hotend before tightening the FlowTech nozzle." Its product page says the FlowTech combines nozzle and thermal break into "one permanently sealed assembly."
• CR-6 SE hotend. Micro Swiss calls the hot step "a critical step to avoid filament leaking." It also says the heater cartridge "might become loose after initial heat up," so check it's fully tightened.

Bambu's hotends work differently. Bambu says they "can be installed when cold," which "eliminates the problems associated with filament oozing or leaking between the nozzle and the heat break interface." On the X1 and P1 series, it says to tighten the two hotend screws evenly, "ensuring not to overtighten." On the A1 series, press the heatsink so it "sits flush against the hotend heating assembly." If the buckle won't lock easily, Bambu says to check that the nozzle is seated flat and the heatsink aligned. It gives two signs of a good install: "no wobble," and the printer extrudes filament properly. If residue stops an old hotend coming out, Bambu says to cut leftover filament off the top of the hotend "to ensure proper reinstallation."

If plastic is already seeping out, our nozzle leaking guide has the full fixes for each hotend.

Step 5: Use a layer height that suits the new size

A layer height chosen for the old nozzle may not suit the new one.

• Bambu Lab. Bambu's nozzle page gives layer heights of 0.05 to 0.12 mm for a 0.2 mm nozzle, 0.1 to 0.3 mm for 0.4 mm, 0.15 to 0.45 mm for 0.6 mm, and 0.2 to 0.6 mm for 0.8 mm.
• PrusaSlicer. Prusa says "you can't print with a layer height bigger than your nozzle diameter," and that your layer height should be "70-80% of your nozzle diameter at maximum, otherwise, the layer adhesion will be significantly compromised." For extrusion width, it says you generally want "about 110% of your nozzle diameter."
• Bambu Lab 0.2 mm nozzles. Bambu says the main speed limit is the Maximum Volumetric Speed in Bambu Studio, and that 2 mm³/s "works with most compatible filaments." It warns that pushing filament through a very small nozzle "can lead to extruder skips, filament grinding or inaccurate extrusion."

Our nozzle sizes guide compares the ranges each maker gives for every size.

What changes with a hardened or wear-resistant nozzle?

The temperature notes we found for hardened nozzles are each tied to specific parts:

• Prusa, for the E3D hardened steel V6 nozzle. Prusa says hardened steel "has different thermal conductivity properties than brass," so you may need to "increase the hotend temperature by about 5°C." It adds that some standard materials, like ABS, "cannot be printed as fast as a regular nozzle."
• E3D, for hot-tightening. E3D's V6 guide heats hardened steel nozzles to 20 °C above printing temperature for tightening, not to the 285 °C it uses for brass.
• Prusa MK4S and MK3.9S. Set the Hardened steel option to ON under Settings → Hardware → Printhead.

Bambu's nozzle page says its hardened steel nozzles suit abrasive filaments, but we didn't find a Bambu temperature adjustment for them. Don't borrow Prusa's figure for other hotends. For help choosing a nozzle, see how to choose a replacement nozzle and our replacement nozzle shortlist.

What if the new nozzle is the problem?

Prusa says in its MK2.5/S, MK3/S/+, MK3.5/S and MINI nozzle guides that the stock brass nozzle lasts "many hundreds of printing hours" unless you print abrasive materials with it, and that changing a relatively new nozzle "to resolve a clog is not the solution!" If you swapped nozzles to cure a clog and prints are still poor, work through clog diagnosis instead.

Bambu's flow rate calibration page suggests the opposite test: "using a new nozzle can confirm if the issue is related to the nozzle, or to calibration." If a known-good nozzle prints well with the same settings, the new one may be faulty or the wrong type for your hotend. If you're not sure whether the old nozzle was worn, our worn nozzle guide covers how to check it.

Checklist

• Nozzle size, and type where your printer asks for it, set on the printer.
• Slicer profile matches the new diameter, and on Prusa printers whether it's high flow.
• First Layer Calibration redone on the Prusa MK2.5/S, MK3/S/+, MK3.5/S and MINI.
• Flow Dynamics Calibration rerun on Bambu Lab printers, manually for a 0.2 mm hotend.
• Nozzle tightened or seated as your maker documents, with no leak above the tip.
• Layer height within your maker's range for the new size.
• Extrusion checked after the swap before a long print.

How this guide was checked

This is a research-based guide. We haven't changed nozzles on these printers for it. Every menu path, temperature, torque and calibration step comes from the Bambu Lab, Prusa Research, E3D, Micro Swiss and Creality pages listed in the sources, retrieved on 2026-10-13. Steps are kept to the printer models and hotends each source names. Read more in our editorial standards.

Nozzles: what to check before you buy ↗ Print problems: what to check before you buy ↗