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UM2+ filament got stuck in hotend

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Hello everyone !

I know the topic is dealt in somewhere on the internet and on the community but I am still a bit confused and I still do not really know the root cause (and probably causes) of the problem... Could you help me please ?

Every 3/4 hours of printing, the hotend gets jammed, and the filament looks like this ->



The jamming is provoked by the thick section in the middle of the picture. The ring at the left occurs only when the hotend cools (I have to cut the tip everytime I want to start a new print). I do not really care about the left ring, the real problem is the thick section in the middle, I cannot print anything at the moment.


The heating block is stock, as well as the heating cartridge and the sensor. For the other parts, they were changed 300 hundreds printing hours ago :

- steel coupler (http://3dsolex.com/product/steel-coupler-v2-for-um2/)

- ptfe coupler (http://3dsolex.com/product/ptfe-coupler-um2/)

- 0.4 nozzle (http://3dsolex.com/product/rsb-0-40mm-nozzle/)

- bowden tube (http://3dsolex.com/product/bowden-tube-clips/)


Does anyone has an idea ? Thank you !

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It looks like your bowden tube probably isn't seated all the way. It can get stuck on the metal plate when you go to insert it. If it does, then there's space (where your spacer is above the coupler), where the filament could expand due to the heat because there's no tube to force it to hold its shape. 


If you're having trouble getting it seated all the way, you might try loosening the thumbscrews a little to give you a bit of flexibility. 

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Thanks to your comment I tried two things : the one you said and the exchange of the PTFE coupler with the old stock one I had. And here is the conclysion: it appears that the 3D Solex PTFE coupler is ageing very badly...

So the interior of the coupler is degrading, letting the PLA to expand. And the tip of the coupler is somewhat shrinking so the ring can appear. 


I'll make other tests to be sure btw. Thank you very much @fbrc8-erin !!


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Worn out couplers can definitely cause expansion. I'm not sure how long the 3D Solex ones are usually good for (I use the Ultimaker ones). Depending on what sort of filament you're using, that can also make a big difference--anything high heat or abrasive is going to put that much more wear on your coupler.

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