How to Change a 3D Printer Nozzle: Heat-Up, Tools, Tightening and Leak Check

When to replace a nozzle instead of cleaning it

Prusa's documentation gives two reasons to swap a nozzle: it's worn out, or you want to print with a different nozzle type or diameter. Wear usually builds up slowly. Fine details get softer and extrusion turns inconsistent, even though your filament and slicer settings haven't changed. Abrasive filaments such as fiber-filled or glitter blends speed this up on a brass nozzle.

A nozzle that won't extrude at all isn't necessarily dead. Before you take anything apart, try clearing it. Prusa lists a cold pull as an optional step right before a nozzle change, and that alone can sometimes restore flow. Our clogged nozzle guide walks through the options. If the problem keeps coming back or the tip is visibly damaged, replacing the nozzle is the simpler fix. If you're switching sizes, read up on 3D printer nozzles before you order.

Figure out which hotend you have

The procedure depends on the hotend. According to Prusa, the Original Prusa MK2.5/S, MK3/S/+ and MK3.5/S use an E3D V6 hotend, so any E3D V6-compatible nozzle will fit. They ship with a 0.4 mm brass E3D V6 nozzle. Prusa's procedure covers every nozzle except the Olsson Ruby.

Newer Prusa machines work differently. Prusa says every MK4S, MK3.9S, MK4, MK3.9, XL, CORE One/+, CORE One L and Signature Oak ships with the Prusa Nozzle, either installed or included in the kit. Each model has its own guide. There's also a second method that uses a Nozzle Replacement Tool, which you print first from Printables, to make the job quicker and easier.

Other brands vary. Some let you swap just the nozzle, while others expect you to replace a larger assembly. Check your manufacturer's manual before you buy parts. If you can't decide between the two approaches, see complete hotend vs. individual parts.

Tools to lay out before you heat anything

For the MK3 family, Prusa lists four items. A 2.5 mm Allen key removes the print fan and its shroud. A 7 mm wrench or socket unscrews the nozzle, and pliers work if you don't have one. A 17 mm wrench, or an adjustable wrench, holds the heater block steady. And a small plate or a sheet of aluminum foil gives you a non-flammable spot to set down a hot nozzle.

Only the Allen key comes with the printer, whether you bought a kit or an assembled unit. You have to supply the 7 mm and 17 mm wrenches and the non-flammable surface yourself, so gather them first. Once the nozzle is hot, you don't want to be digging through a drawer.

Don't skip the 17 mm wrench. Without it, the heater block turns with the nozzle, and the whole hotend takes the strain, wiring included. Holding the block firmly keeps the unscrewing force on the nozzle threads, where it belongs.

Why the nozzle has to be hot, and how hot

Start by unloading filament from the LCD menu with Unload Filament. A cold pull is optional at this stage. On firmware 3.12.0 or newer, the printer then displays a message linking to Prusa's guide. Click the LCD knob, and the printer homes itself, raises Z to the top, centers X, and heats the nozzle to 280 °C automatically.

The MK3.5/S is slightly different. You raise the extruder yourself through Control, Move Axis, Move Z, then preheat the nozzle to 280 °C from the Temperature menu. If you're on older firmware, Prusa recommends updating first. Otherwise, follow the alternative step in its guide.

Prusa calls heating the nozzle essential to the process. When it's hot, leftover plastic in the threads stays soft, so the nozzle comes out without brute force. Keep in mind that 280 °C is Prusa's figure for these specific models. On any other printer, use the temperature your manufacturer specifies and stay within what your hotend is rated for.

Removing and installing the nozzle step by step

Once the nozzle reaches temperature, remove the two screws on the print fan and the single screw holding the fan shroud, then take both parts off. That gives you access to the nozzle. Grip the heater block with the 17 mm wrench. Unscrew the nozzle with the supplied pliers, or with a 7 mm wrench or socket if you're using E3D nozzles. The nozzle is still hot, so set it straight down on your plate or foil and let it cool out of the way.

Before you install the new nozzle, confirm the printer is still on the same screen and the target is still 280 °C. Keep the wrench on the heater block, thread the new nozzle in carefully, then tighten it gently but firmly. Prusa is explicit about this: don't use excessive force. Cranking harder can damage the threads, and it won't make the seal any better.

Reinstall the shroud and fan with their screws, and check that no wires get pinched along the way.

The final check that prevents leaks

This is where most nozzle swaps that end in a leak go wrong. Prusa says there must always be a small gap, about 0.5 mm, between the nozzle and the heater block. The nozzle shouldn't bottom out on the block. It needs to be tightened into the block and locked against the heat break while hot. If you skip that, molten plastic finds a way out around the threads.

In practice, look at the nozzle from the side after you tighten it. If you can't see daylight between the hex and the block, the nozzle is probably resting on the block instead of the heat break. Back it off, thread it in again, and retighten while hot. Plastic oozing around the block during your first few prints is a warning sign you shouldn't ignore.

Afterward, reload filament and recheck your first layer, since the nozzle height may have shifted slightly. Our 3D printer calibration guide covers that step.

Sources and limits

• Prusa Knowledge Base — Changing or replacing the Prusa nozzle
• Prusa Knowledge Base — Changing or replacing the nozzle (MK2.5S/MK3S/MK3.5S)

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.