Stuck nozzle — heat sink replacement — Oh what fun
 
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fuchsr
(@fuchsr)
Famed Member
Stuck nozzle — heat sink replacement — Oh what fun

My single-tool XL has been sitting idle for a few weeks. Why? After swapping nozzles a dozen times with no issues, last time the nozzle gets stuck in the heat sink. Heater block with nozzle just won't come out. After some increasingly impatient prodding, pulling and twisting, the nozzle finally snaps where the metal part turns into what looks like copper:

(Ignore the "bite marks" on the nozzle. They're a result of trying to get the nozzle out after disassembly).

At this point came the realization that I'd have to replace the heat sink. Of course, it wasn't in the Prusa store so my printer had become a brick.

Well, last week I checked again, and voila, there it was available now and I ordered it right away.

I finally had time today to install it. Searched the Prusa knowledgebase for "replace XL heat sink". No dice. Got on the chat with Prusa Support to see if there's a hidden document somewhere, or they could share their internal assembly manual. No luck. They referred me to the Mk4 assembly instructions, but the Mk4 hotend looks quite a bit different even though it uses the same heat sink.

So I was on my own. Taking pictures at each step I was able to take this thing apart and successfully put it back together again. Took an hour or so. And had to do it again because I had forgotten to swap the grub screw that holds the nozzle in place from the old to the new heat sink ☹️😡

But when everything was done, miraculously the printer started up fine and passed all tests. Well, it failed the filament test but apparently that's a common issue. After restarting the printer it passed the test eventually.

Even with the heat sink removed I can't really see why the nozzle didn't come out. The most likely culprit — and I hate to say that because if true I can't blame Prusa, only myself — is that the grub screw that holds the nozzle in the heatsink was tightened too much and had deformed the nozzle shaft. I have a hard time seeing how I could possibly have deformed it to the point that the nozzle wouldn't come out, but I don't see any other explanation.

If any unfortunate soul ends up in the same situation, DM me and I'll send you a step-by-step guide with pictures.

Posted : 23/10/2023 9:55 pm
MikeH and ssill2 liked
ssill2
(@ssill2)
Noble Member
RE: Stuck nozzle — heat sink replacement — Oh what fun

yep, you've convinced me that if I need to do nozzle swaps I'll be buying whole heatblock + nozzle assemblies to do it with lol

Posted : 23/10/2023 11:40 pm
fuchsr
(@fuchsr)
Famed Member
Topic starter answered:
RE: Stuck nozzle — heat sink replacement — Oh what fun

Would have made a difference. The part stuck in the heat sink was the long rear shaft of the Prusa nozzles. So changing nozzles or changing the heater block assembly, would have been all the same. 

Posted : 23/10/2023 11:53 pm
ssill2
(@ssill2)
Noble Member
RE: Stuck nozzle — heat sink replacement — Oh what fun

My sincere hope is I won't be messing with it all that much.  I'm not professional printer like you and others on here lol I think I changed the nozzles just a couple times on my MK3S printers and that was only to put a hardened steel nozzle on there so I could print some glow-in-the-dark PLA.   I'm hoping that over time they make it easier for folks like you who do them frequently.  the one time I did it on the MK3 and got a leak really made me gun shy about doing it.

Posted : 23/10/2023 11:56 pm
xenon
(@xenon)
Trusted Member
RE: Stuck nozzle — heat sink replacement — Oh what fun

tightened the screws a bit too much so it deformed the pipe?

Posted : 24/10/2023 10:36 pm
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