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How to replace a hotend assembly (MK4S / MK3.9S)

How to replace a hotend assembly (MK4S / MK3.9S)

How to replace a hotend assembly (MK4S / MK3.9S)
Relevant for:
Last updated 9 days ago
How to replace a hotend assembly (MK4S / MK3.9S)
 Difficulty
Very easy
 Steps
15
 Available languages
CSPLDEITFR
Introduction
Introduction
This guide will take you through the Hotend assembly replacement on your Original Prusa MK4S or MK3.9S.
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.
Preparing the printer
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.
Protecting the heatbed
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.
Disconnecting the hotend cables
Disconnecting the hotend cables
Disconnecting the hotend cables
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.
Removing the hotend
Removing the hotend
Removing the hotend
Remove the hotend cables from the cable channel.
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.
Hotend assembly parts preparation
Hotend assembly parts preparation
For the following steps, please prepare:
MK4S Hotend assembly (1x)
The MK4S hotend assembly has a Nextruder Silicone Sock installed by default. It is optional, and you can remove it at any time.
For more information, read the article Nextruder Silicone Sock.
Inserting the hotend
Inserting the hotend
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.
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!
From the underside, check that the hotend is oriented correctly. It must fit between the cutouts in the X-carriage.
Nozzle insertion check
Nozzle insertion check
Nozzle insertion check
Verify that the nozzle is fully inserted. The copper ring on the nozzle should not be visible if it’s properly seated.
If not fully inserted, poor heat transfer may occur, potentially leading to issues like nozzle clogs.
To adjust the nozzle position, loosen the thumbscrews, reposition the nozzle, and then retighten the screws, while pushing the hotend assembly up.
Guiding the hotend cables
Guiding the hotend cables
Guiding the hotend cables
Locate the cable channel behind the thumb screws. Guide the hotend thermistor cable through the channel first. Then insert the hotend heater cable.
Guide the hotend fan cable as seen in the picture. Push it in the cable channel.
Connecting the hotend
Connecting the hotend
Connecting the hotend
Connect the hotend thermistor to the top left slot on the LoveBoard.
Connect the hotend heater to the black slot on the upper part of the LoveBoard.
Arranging the cables
Arranging the cables
Arranging the cables
Arranging the cables
Arrange all the cables according to the picture (view from above). All cables must be squeezed as close to the extruder body as possible.
Close the Fan-door-cover.
Slide the Loveboard-cover on the extruder. And push it down.
Be careful not to pinch any cables!
When the cover is properly and completely inserted, you will feel a slight "click" of the rear latch.
Setting up the nozzle diameter
Setting up the nozzle diameter
Setting up the nozzle diameter
Setting up the nozzle diameter
This step is important only if you changed your nozzle diameter or type.
Visit the Settings > Hardware menu
Select the Nozzle diameter you are using (e.g. 0.25 / 0.3 / 0.4 / 0.5 / 0.6 / 0.8)
On MK4S, the 0.40mm is the stock nozzle size.
Turn on the silicone sock option if you are using one.
Select a Nozzle type, if you switched switched between the Normal nozzle and a high flow version.
Final check
Final check
Final check
To check if everything is connected correctly go to Control > Temperature > Nozzle Temperature and set it to a temperature above 200°C.
Go back to the main screen and check the bottom bar to see if the temperature rises.
That's it!
That's it!
Great job! You just successfully replaced the Hotend assembly on your Original Prusa MK4S.
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