Filament leaking around the nozzle: loose nozzles and hotend gaps

This guide is for anyone finding a crust of plastic building up around the nozzle, on the heater block, or inside the silicone sock. It explains why the seal fails, the hot-tightening steps E3D, Prusa, and Creality document for their hotends, how Bambu Lab's one-piece hotends differ, and when a replacement part makes more sense than another retightening.

Leaking, oozing, or a clog?

These look alike at first, but they have different fixes:

If you see signs of both, clear the clog with your maker's procedure and then fix the seal.

Why does the seal fail?

On a screw-in hotend like the E3D V6, the heater block holds the nozzle, but the seal is made where the top of the nozzle presses against the bottom of the heat break. Prusa's MINI guide says the nozzle must be "'locked' against the heatbreak, creating a seal." The common ways that goes wrong:

• The nozzle was tightened cold. Prusa says V6 nozzles on the MK3 family and MINI/+ need tightening while hot, or a gap opens between nozzle and heat break "through which the filament will leak out."
• The nozzle bottomed out on the heater block. Prusa says there must always be a gap of about 0.5 mm between the nozzle and the heater block. On the MINI, it says that if there's no visible gap, the nozzle may not have reached the heat break, "which can lead to leaks and clogs." On the MK2.5, MK3, and MK3.5 families, it says failing to lock the nozzle against the heat break "will cause leaks."
• The gap is too large. Prusa's MINI guide adds that a gap of several millimeters "can change the thermal properties of the hotend," and the printer may struggle to reach and hold temperature.
• Too much force. E3D warns that over-tightening a V6 nozzle risks "shearing either the nozzle or HeatBreak." A sheared or damaged part can't seal, however carefully you tighten it.
• The wrong nozzle family. E3D sells V6, MK8, and Revo nozzles as separate lines, and lists its V6 nozzles for the V6, Lite6, Chimera, Titan Aero, Titan Aqua, Hemera, Prusa MK3, and Prusa Mini. Prusa says its Nextruder printers use the Prusa Nozzle and need the Nextruder V6 Nozzle Adapter to take V6 nozzles. A nozzle from the wrong family isn't covered by the maker's sealing procedure, so match it to your hotend first. Our replacement nozzle guide explains how.

Fixes by hotend

Use the procedure for your exact printer and hotend. The numbers below apply only to the hardware each source covers.

E3D V6 nozzles

E3D's V6 hot-tightening guide says that, for brass nozzles, you heat the hotend to 285 °C and wait about a minute so the parts reach the same temperature. Then tighten using a 7 mm spanner and an adjustable wrench. For its plated copper, hardened steel, Nozzle X, and ObXidian V6 nozzles, E3D says to heat to 20 °C above your printing temperature instead. For every material, it says: "You are aiming for 2Nm of torque," and it recommends a torque wrench set to 2 Nm if you're unsure.

Prusa MK2.5/S, MK3/S/+, and MK3.5/S

These printers use the E3D V6 hotend. Prusa says to "follow this procedure exactly," because skipped steps "can cause leaking and extrusion issues." In outline:

1. Unload the filament. On the MK2.5/S and MK3/S/+ (firmware 3.12.0 or later), use LCD Menu > Settings > HW Setup > Nozzle Change, which heats the nozzle to 280 °C. On the MK3.5/S, raise the extruder and preheat the nozzle to 280 °C manually.
2. Remove the print fan and fan shroud. Hold the heater block with a 17 mm spanner and remove the nozzle with pliers or, for E3D nozzles, a 7 mm spanner or socket.
3. With the nozzle still at 280 °C, screw the new one in "gently, but firmly." Prusa says its service and assembly teams use a torque wrench rated for 1–5 N m and tighten the nozzle to 2.5 N m.
4. Check for the roughly 0.5 mm gap between the nozzle and the heater block.
5. Redo the First Layer Calibration afterward.

Prusa MINI/MINI+

Prusa says to preheat the nozzle to 280 °C and raise the extruder, then turn off the printer before touching the nozzle. While the print head is still hot, hold the heater block with a 16 mm spanner or adjustable wrench, and use pliers or, preferably, a 7 mm socket on the nozzle. Tighten "gently, but firmly," and stop once it won't go further. Then check for the same slight gap above the nozzle and redo the First Layer Calibration. Prusa's MINI guide doesn't give a torque figure.

Prusa Nextruder printers (MK4/S, MK3.9/S, XL, CORE One)

These printers use the Prusa Nozzle, not a plain V6 nozzle. Prusa says the replacement method "varies depending on the model," and links a separate guide for each printer, plus a printable Nozzle Replacement Tool. Don't apply the V6 numbers above to these printers. Follow Prusa's guide for your model.

Bambu Lab X1 and P1 series

Bambu Lab's hotends are built differently. Bambu says its hotend is "a single unit, incorporating the heatsink, throat, heater block, and nozzle." It can be installed cold, which "eliminates the problems associated with filament oozing or leaking between the nozzle and the heat break interface." There's no nozzle to hot-tighten. To change it, Bambu says to set the hotend to 50 °C or lower, power off, unplug the heater, fan, and thermistor cables, and remove two screws.

Bambu sells two replacement options, the Hotend with Nozzle and the Complete Hotend Assembly. The Complete Hotend Assembly comes in separate X1 and P1 versions, and the X1 version fits the X1 and X1C, not the X1E. If residue stops the hotend coming out, Bambu says you can heat it slightly, wear heat-resistant gloves, and pry it loose gently. Then cut off any leftover filament at the top so the new one seats properly.

Bambu Lab A1 series

The A1's hotend is toolless and held by a buckle. Bambu says to power off and make sure the nozzle isn't hot before removing it. When refitting, 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 is aligned. A good install shows no wobble and extrudes properly. Bambu notes that the A2L has its own guide.

Creality K1

Creality says the K1 uses an integrated nozzle. Its procedure heats the nozzle to 220 °C and holds it at that temperature. You hold the nozzle with the wrench from the toolkit and loosen or tighten it with a socket, never by hand. Afterward, check that filament extrudes normally before refitting the silicone sleeve with the printer powered off and cooled. We didn't find a torque value in Creality's K1 guide, so don't borrow E3D's or Prusa's figures.

When should you replace parts?

Retightening fixes a leak caused by a nozzle that wasn't hot-tightened. Replacement makes more sense when:

• A part is damaged. If a nozzle or heat break has sheared or won't seal, which E3D warns over-tightening can cause, replace it rather than adding torque.
• You have a one-piece hotend that still leaks. Bambu says its one-piece design eliminates leaking between the nozzle and heat break, and it doesn't document a tightening fix, so open a support ticket first. On Bambu Lab printers, the nozzle comes as part of the hotend, so any replacement is a Hotend with Nozzle or a complete assembly for your exact series. Bambu lists severe clogs, wear from abrasive materials, and hotend damage as reasons to replace a hotend.
• The nozzle is worn or the wrong type. For its MK3-family printers, Prusa says the stock brass nozzle lasts "many hundreds of printing hours" unless you print abrasive materials with it. It also says that changing a relatively new nozzle "to resolve a clog is not the solution." Our worn nozzle guide covers how to check for wear.

Buy parts that match your exact printer and hotend. Our replacement nozzle guide covers fit, and our replacement nozzle shortlist groups options by the printers each maker lists. After any nozzle change, follow your maker's post-change steps, such as Prusa's First Layer Calibration on the MK3 family, or, if you fitted a Bambu Lab hotend of a different diameter or material, updating the nozzle information on the printer's screen.

A sensible order

1. Confirm it's a leak above the tip, not ooze from the tip or a clog.
2. Check that your nozzle is the right family for your hotend.
3. For V6-style hotends, heat to your maker's temperature and hot-tighten to its torque, keeping the gap above the heater block.
4. For one-piece hotends, power off, reseat the hotend as your maker documents, and check it sits flush.
5. If it still leaks, inspect for damage and replace the nozzle, heat break, or hotend your maker specifies.
6. If extrusion was also weak, work through clog diagnosis.

Nozzles: what to check before you buy ↗ Tools: what to check before you buy ↗