I suggest just "print it out" at one point the broken area will be out if the nozzle and everything is in one piece again. Then you can make cold pulls and it all sticks together...
Thanks for the idea! Unfortunately, the piece is jammed, and even when I pressed on it with a screwdriver, it wouldn't extrude.
I'm about to buy another BB core... but before I do, what can I do to get that piece of filament out? I really don't want to have to buy one.
A few suggestions:
- contact your reseller. He's your primary source for help.
- Maybe you can press a piece of filament with a molten tip in the core, to fuse it against the piece of PVA in the core. Make sure the core is in the printer, and heated to 220 degrees or so, and bowden tube disconnected. You might be able to pull it loose.
- Last resort: heat it up to 250 degrees, and press really hard with some other piece of filament (use pliers so your don't get injured when the filement breaks). Make sure the printhead is in one of the corners, so not to bend your axes.
What about just pushing in a thin metal wire from the under side while pushing fillament from the top like tom's says.
For 0.4 mm you can f.e use 1 strand from a metal brush or a acupuncture needle.
Hey @tomnagel, @ultiarjan,
Thanks for the suggestions! I did contact the reseller... they thought I should just get a new print core. I'll try your second suggestion, @tomnagel, but it's really stuck in there. Last resort has already been passed: except at max temp. Nothing came out except smoke. I tried the wirebrush method... there isn't even any filament in the heated nozzle. As far as I can tell, the filament's tip was hot, and it somehow might've cooled down in the section of the print core with the heat sink. I'm not sure.
well if all else fails, you at least have some spare parts 
seriously if you want to attempt to take the thing apart have a look at this first;
edit: somehow inserting this video does not work.... but the above link does...
1
What about warming up the core without the fan connected, not too warm to avoid to burn the filament, but long enough to warm up the upper part of the core and soften the part which is stuck...
If you give the core for loose, try crazy ideas. Ofc @amedee trick could work. Also, a 2-2.5mm drill bit could work if you have a steady hand. After all, you need to just measure the distance so you never drill near the heat break. After removing or making a hole, put it on the printe, heat, and do the atomic method described on the um3 guides. I think you could fix it.
Hi RayvenMaker,
Why not try your first method?? This is not high class electronics, just a wire wound heat element and a PT100 temp sensor, well plus a contact.
All of this can stand 60 deg. C. water, no problem.. But after this bath, -put it in to a "hot air" oven with about (50-60) deg. Celsius for an hour or so. Next is to heat it up some in the normal way. This is the method that's less risky and do not ruin your day!
Sure, I'm assuming there's no active electronics in this unit.
Well, as neotko "said", -crazy ideas might not be as bad as most people think -it's only a little different way of thinking.
Oh yes, been working most of my life with electronics so this should be an easy one.
OK., good luck.
Thanks.
Torgeir.
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You could just ship it to me at thegr5store.com and buy the hardcore upgrade. Then in the future you can just swap nozzles. I know some people have printed PVA in the "race" nozzles that come with the hardcore and it worked "fine" but there is a danger, heck it's likely, that the PVA will slowly clog it up over the years but you can just change the nozzle in minutes and they cost "only" $22 at this time.
If you live in Boston Area and bring it by my house I'd be happy to take it apart for free and fix it. I've taken apart quite a few cores now including ones all gummed up with filament. I've got tricks...
Ok, just took apart the print core... here are some photos of the parts with the PVA.
Yeah, it's really stuck. 
I'm letting the two parts soak in water, and I'll see if that helps. If it doesn't get that caramelized part out, I'm going pro and drilling it out.
Thanks for all the help! I couldn't have done it without you guys.
Make On!
RayvenMaker
1
Let it soak at least 12 hours. And every 4 hours or so stick a toothpick in there and pull some out.
Cook in water!
Now I don't own a UM3 - but I've had some severe nozzle blockages too on my 2's. Faced with either tossing the nozzle in the bin or trying out "alternative medicine" I've found that extreme heat works very well to clear bits of filament that are well and truly stuck. I've very good experiences applying a small blowtorch to the nozzle until whatever's in there simply drips out. Sometimes a few bits of burnt residue remains and need to be cold pulled afterwards, but other than that the nozzles have been working like new afterwards. It did appear rather extreme to me when I tried it... but I have suffered zero issues from it so far.
Ok, just reassembled the print core. I put it back in the printer, and tried to run some cleaning filament through it... all that came out was this coarse, orange, fragile powder that no one could call proper extrusion. Tried the atomic method—it seemed like it couldn't get a good grip.
Someone had to drill (or CNC) that 0.4mm hole in the nozzle (unless it was injection molded with some serious black magic), so there's probably a 0.4mm mill bit out there, right? Where could I find one... if that's a good idea.
What about replacing just the nozzle? I think I saw one on @gr5's store—would that fit in my existing heater block?
@SyntaxTerror, I've tried blowtorching before, back with my Ultimaker 2... ended up warping the nozzle. But there was a lot of filament jammed in there, and I probably got it too far into the red-hot spectrum... there isn't much left in this nozzle, so I think I'll give it a shot, last resort.
Make On!
RayvenMaker
Hehe, well just go easy on it. We don't need red hot for the filament to get runny... just hotter than usual
@RayvenMaker - sorry no those nozzles aren't long enough in the threads. But I *do* sell the hardcore which is like a UM core but where you can change nozzles easily. And I'll sell you just a DIY kit since I know you now know how to take it apart and put it together without breaking the delicate steel core. Or you can get a complete core already with the hardcore from my store and I'll pay you for your broken BB core. Or you can send in your broken BB core and I'll upgrade it. 3 choices for you if you are interested.
@RayvenMaker - sorry no those nozzles aren't long enough in the threads. But I do sell the hardcore which is like a UM core but where you can change nozzles easily. And I'll sell you just a DIY kit since I know you now know how to take it apart and put it together without breaking the delicate steel core. Or you can get a complete core already with the hardcore from my store and I'll pay you for your broken BB core. Or you can send in your broken BB core and I'll upgrade it. 3 choices for you if you are interested.
Sorry that I didn't get back to you sooner... I've been busy. I'll see what happens after I blowtorch it... But I think I might just want to buy a new BB core. Right now, I'm working with fbrc8 to get this straightened out—I only got this in November. Also, I'm probably not going to use my BB very much, so it doesn't really make sense for me to make it really versatile.
But actually, I'm looking into the upgrade for one of my AA cores—I loved being able to change nozzle sizes and hardnesses back with my UM2 (with Olsson block). CF filament has always been on my 3DP wishlist...
Make On!
RayvenMaker
Edited by Guest@RayvenMaker just a note. Never, ever, never, also never ever ever, use any 'cleaning filament'. They don't explain how the chemicals can bond with others and you can end up having to trash it. Also since the um3 doesn't has a full ptfe heatbreak but a very thin steel between the ptfe/hotzone it can be very very dangerous to atomic pull a cleaning filament because it can cold very fast on the heatbreak or mix with the residue + coldfast. If that happens you just need to forget about it or drill until the end of time itself...
I say this because last time I used cleaning filament was once after using a CF filament and the mix made a cement so fast that I broke one of the first Ruby Nozzle betas. So, stay away from the cleaning filaments.
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Good to know. I sometimes use nylon as a "cleaning filament". I don't know what those cleaning filaments are made of.
@RayvenMaker just a note. Never, ever, never, also never ever ever, use any 'cleaning filament'. They don't explain how the chemicals can bond with others and you can end up having to trash it. Also since the um3 doesn't has a full ptfe heatbreak but a very thin steel between the ptfe/hotzone it can be very very dangerous to atomic pull a cleaning filament because it can cold very fast on the heatbreak or mix with the residue + coldfast. If that happens you just need to forget about it or drill until the end of time itself...
I say this because last time I used cleaning filament was once after using a CF filament and the mix made a cement so fast that I broke one of the first Ruby Nozzle betas. So, stay away from the cleaning filaments.
Good tip! I'm going to be a little more cautious about using it now...
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I suggest just "print it out" at one point the broken area will be out if the nozzle and everything is in one piece again. Then you can make cold pulls and it all sticks together...
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