How to replace a hotend assembly (MK4 / MK3.9)

Relevant for:

MK4 MK3.9

Last updated 5 months ago

Difficulty

Very easy

Steps

Available languages

Step 1 Introduction

⬢This guide will take you through the Hotend assembly replacement on your Original Prusa MK4 or MK3.9.

The following instructions are compatible with all Prusa Nozzle diameters.

⬢All necessary parts are available in our eshop prusa3d.com.

Note that you have to be logged in to have access to the spare parts section.

Step 2 Preparing the printer

⬢Unload the filament from the printer.

It's recommended to take off the spool holder from the printer.

⬢Move the Z-axis to the center position to easily access the extruder from the top and bottom.

Step 3 Protecting the heatbed

⬢Turn the printer OFF and unplug the power cable from the PSU (Power Supply Unit).

Make sure the printer parts - print head and heatbed are cooled down at room temperature.

Before proceeding any further, it is recommended to protect the heatbed first!

⬢Take off the flexible steel sheet.

⬢Use any cloth or piece of fabric, which is thick enough and cover the heatbed. This will ensure you won't damage (scratch) the surface during the disassembly.

Step 4 Accessing the hotend cables

⬢Slide the Loveboard-cover up and remove it from the extruder. There are two cutouts on the back of the part, which you can grab for easier removal.

⬢Open the fan-door widely.

Step 5 Disconnecting the hotend cables

Each connector has a safety latch. It is necessary to press the latch before disconnecting. Otherwise, the connector may get damaged.

⬢Disconnect the hotend heater cable.

⬢Disconnect the hotend thermistor cable.

⬢Remove the heatsink fan cable, hotend thermistor, and hotend heater cables from the cable channel and leave them free for now.

Step 6 Removing the hotend

⬢Grasp the hotend with your hand.

⬢Use your other hand to loosen the two thumb screws. There is no need to remove them completely, a few turns are enough.

⬢Slide out the hotend assembly from the heatsink.

⬢At the same time push the hotend cables behind the heatsink out of the extruder.

Step 7 Hotend assembly parts preparation

⬢For the following steps, please prepare:

⬢Hotend assembly (1x)

The Hotend assemblies with different nozzle sizes are available on the Prusa E-shop.

Step 8 Inserting the hotend

⬢Locate the corresponding opening on the bottom of the extruder heatsink and insert the hotend into the heatsink.

⬢At the same time, push the hotend cables behind the heatsink fan up towards the electronics.

⬢Push the hotend assembly all the way into the heatsink. There should be approximately a 2 mm gap between the heatsink and the brass part of the nozzle.

⬢Orient the hotend assembly so that the HOT symbol on the heaterblock faces forward.

⬢While pushing the hotend assembly in, firmly tighten the lower thumb screw and the upper thumb screw. Avoid pinching any cable between the screws and the heatsink!