⬢This guide will take you through the replacement of the hotend thermistor on the Original Prusa MK4 and MK3.9.
Thermistor Info: There are several variations of the thermistor, which may differ in length and color depending on the manufacturer. Functionally they are the same.
⬢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.
WARNING: The hotend and heatbed are very HOT. Do not touch these parts!!!
⬢For the following steps, it is necessary to have the heaterblock and the hotend clean from the remains of the filament.
If you have a Prusa hotend sock on the hotend, remove it.
⬢On the printer screen, go to Control -> Temperature -> Nozzle Temperature and using the knob set 250°C.
⬢Wait at least 5 minutes. The remains of the filament must be warmed up slightly so that they can be removed more easily.
⬢Using the brass brush, carefully clean the heaterblock and the hotend from the filament residue. Avoid contact of the brush with the hotend cables, as this could cause a short circuit.
⬢When the heaterblock and the hotend are perfectly clean, cool down the printer. On the screen, navigate to Preheat -> Cooldown.
Wait until the hot parts are cooled down to ambient temperature. It takes approximately 10 minutes.
⬢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.
Turn the printer off and unplug it from the socket!
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.
⬢Locate the hole in the heatsink from the bottom of the extruder and insert the hotend into the heatsink.
⬢At the same time, push the hotend cable behind the heatsink fan up to 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!
⬢Arrange all the cables according to the picture. All cables must be squeezed as close to the extruder body as possible so as not to interfere with the cover in the next step.
⬢Great job! You just successfully replaced the hotend thermistor on your Original Prusa MK4/MK3.9.
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