The 0.4 mm brass nozzle in my Prusa i3 MK3 is worn out - the extrusion hole is visibly larger than the replacement nozzles I have to fit. So I’m trying to replace the nozzle.

Unfortunately the nozzle seems to be stuck in the heater block. So far I’ve tried:

  1. Heating the hotend up to 285 °C, rotating the heater block slightly and trying to unscrew the nozzle with a wrench. (I exactly followed the Prusa YouTube video on changing nozzles).
  2. Leaving the hotend at 285 °C for 15 minutes and trying again - I found some other reports online this had helped. However it made no difference in my case.

In an effort to try and remove the nozzle from the heaterblock, I’ve now accidentally bent the heatbreak, so I’m going to have to replace some or all of hotend. But I need to get the nozzle out, so I know which parts to order - if the nozzle breaks off in the heater block I’m definitely going to need a new heater block as well.

What else can I try to free a seized nozzle?

This is the original factory-fitted brass nozzle, and the hot-end was pre-assembled in the kit I received.

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    $\begingroup$ Make sure you're turning it the right way! If you're looking down at the extruder the nozzle unscrews CW, not CCW. $\endgroup$ – Marquis of Lorne Jan 7 at 3:51
  • $\begingroup$ Good point - however I am definitely rotating the right direction - CW. This is where following videos is a great help. $\endgroup$ – Andrew Ebling Jan 8 at 7:34

Try to, First, remove the heat block from the extruder/heat sink. Then heat the hot end to ~ 230 'C. Then try to unscrew the nozzle while holding the heat block with a wrench or plier. Be extra careful with the heat block and with the plier.

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