Of course, I checked the temperature right after removing the nozzle, the plastic inside was still molten.
Well, first i tried to press "retraction" button in cura, I figured, it would be similar to turning the big gear)) Yes, I pulled it using my hands, really hard, it did not budge.
I really don't understand how can it be stuck. Both abs and pla should be liquid when heated to 245-260 C, and the filament should come out easily...
What can happen is that heat travels up in the system and softens the plastic higher up than it should, that plastic then expands and gets stuck.
To open up the head you unscrew the four large screws. Heat the head up to printing temperature, hold the bowden tube firmly in place (so that it can't move down) and then wiggle the big square metal part (careful, it's hot!) until that whole assembly comes loose. Once you've done that it should be easy to remove the filament.
When you put the head back together again make sure that the bowden tube is seated all the way down into the white teflon part. If it's not, unscrew the four long screws again but only partially, maybe 2-3mm depending on how much you need to move the bowden, then press the bowden down and tighten the screws back up again.
Looking through the assembly instructions will make things clearer: http://wiki.ultimaker.com/Ultimaker_rev.4_assembly:_Extrusion_head
1
You may have 2 problems:
1) Nozzle is clogged.
2) Filament softened in upper head causing it to get stuck.
Robert is mostly discussing problem #2 which seems to be confirmed and is often caused by keeping the head too hot (245C) with PLA in it and with the PLA not being extruded constantly for more than 5 minutes.
Problem #2 maybe have been caused partially by problem #1?
You removed the nozzle. Did you try pushing some PLA filament through it while it was still hot to see if it comes out the tip?
When switching from ABS to PLA it is very common to get nozzle clogs - even hours into the next print. I think bits of ABS get into the feeder bolt and tiny pieces can slowly climb through the bowden and get into the head. I've seen Ultimaker employees - when they switch from ABS to PLA they typically print some junk part for at least 30 minutes and with the head at ABS temperatures (250C?). Occasionally you will see a tiny dot of the ABS color plastic come out the nozzle.
[...]
When switching from ABS to PLA it is very common to get nozzle clogs - even hours into the next print. I think bits of ABS get into the feeder bolt and tiny pieces can slowly climb through the bowden and get into the head. I've seen Ultimaker employees - when they switch from ABS to PLA they typically print some junk part for at least 30 minutes and with the head at ABS temperatures (250C?). Occasionally you will see a tiny dot of the ABS color plastic come out the nozzle.
As I might soon be in a similar situation: Is it rather a question of print time to clean the nozzle from ABS (high probability for the remaining ABS to get proceeded) or does the amount of used filament (e.g. the printing speed / the feedrate) also matter in the described procedure?
You may have 2 problems:
1) Nozzle is clogged.
2) Filament softened in upper head causing it to get stuck.
Robert is mostly discussing problem #2 which seems to be confirmed and is often caused by keeping the head too hot (245C) with PLA in it and with the PLA not being extruded constantly for more than 5 minutes.
Problem #2 maybe have been caused partially by problem #1?
You removed the nozzle. Did you try pushing some PLA filament through it while it was still hot to see if it comes out the tip?
When switching from ABS to PLA it is very common to get nozzle clogs - even hours into the next print. I think bits of ABS get into the feeder bolt and tiny pieces can slowly climb through the bowden and get into the head. I've seen Ultimaker employees - when they switch from ABS to PLA they typically print some junk part for at least 30 minutes and with the head at ABS temperatures (250C?). Occasionally you will see a tiny dot of the ABS color plastic come out the nozzle.
I switch from abs to pla almost every day, it takes some time, but generally it starts printing fine after the color of the extruded plastic becomes "normal" and not mixed with the color of the previous filament. I print with pla at 245 C though, I assume, this may be an issue in case you use lower temperatures.
I have already disassembled the printhead, it turned out, that plastic expanded in the upper part of the printhead causing the jam, just like Robert predicted.
I would like to thank everybody for assistance.
I am printing PLA on an Ultimaker Original; 220C at 25mm/sec.
Print proceeds smoothly for 10-12 hrs and then fails.
A plug forms to restrict filament feed.
Do I need a lower temperature for PLA?
This is a known problem - especially on older UM Originals. It is worsened with lots of retraction as that transfers heat upwards farther and farther like a relay race.
It's possible your head is assembled "wrong". Don't be embarrassed but please supply a photo that clearly shows the PEEK part (that dark brown piece) and pieces in that region including the nozzle and the heated chamber.
220C is fine. I've printed 240C for 2 hours and I've printed 220C for 10 hours before (on UM Original). Do you also have a heated bed or heated chamber? Is your UM in a room that exceeds 30C or 90F? In other words is it very hot there?
Is your bowden tube seated all the way in or could it have slipped upwards a bit leaving a gap for soft PLA to get into?
I use ColorFabb nowadays and have to print PLA at 185C and 40mm/s for some parts to prevent clogs into the bowden tube, resulting in zero extrusion.
I think like Gr5 said, it is due to the retraction (depending on shape of the part) making the plastic to soft above the hot end. So i try to print at low temp. ColorFabb seems to get more soften at lower temp than Ultimaker filament.
Altough i am convinced i never had clogging in the bowden the first couple of years, i need to accept the new situation :(
I already replaced the hotend and bowden a couple of times.
Maybe it is because i print larger parts than before...
I might shop for Ultimaker filament once again. Just to taste the difference!
You could place a fan on the peek/aluminium holder area to keep the heat more stable on the peek/ptfe coupler area. On my magnetic head changer I use a 5v fan focus on that area and I never had any clog. Ofc I have mod it for 1.75mm filament that can use smaller retractions. The only clog I had it's been because the ptfe coupler died. Something will be greatly improved by the TF2K coupler for UMO that @swordriff it's making. Can't wait to have a really long lasting sollution for the coupler.
Edited by Guest
Something will be greatly improved by the TF2K coupler for UMO that @swordriff it's making. Can't wait to have a really long lasting sollution for the coupler.
There goes the secrecy... 
It was a secret?
Shhh then lets keep in silence....
It was a secret?
Shhh then lets keep in silence....
Everything is a secret until it's told in public... 
1
It was a secret?
Shhh then lets keep in silence....
Everything is a secret until it's told in public...
Anyhow I think it's really good news for umo/umo+ users that want something that last longer. But oh umm it's a secret! 
Yeah! In my research I came already across his website.
But i have a UM (custom made +). It is available for UM2... for now as i understand
In the meantime I will tweak some retraction settings (distance, minimal extrusion).
Edited by Guest
1
I experimented with the retraction and temp settings.
What can happen is that heat travels up in the system and softens the plastic higher up than it should, that plastic then expands and gets stuck.
I was having trouble mainly for the first layer with a clogged bowden tube because of expanding filament. Even at 175C the problem occurred.
So i realized it might due to the pressure getting build up rather then heat traveling upwards.
MariMakes posted a topic in UltiMaker Cura,
ArunC posted a topic in UltiMaker 3D printers,
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IRobertI 521
Something to check first, is the nozzle getting up to temperature properly? Try touching a piece of ABS to the nozzle after heating it to printing temp to see that it has actually reached that temperature.
When you say you tried to remove it manually, did you mean by turning the big gear or by opening the feeder latch and pulling on it with your hands? The reason I ask is that if you've only tried by turning the gear it might be that the knurled bolt has grinded the filament down so that it can't properly grab it anymore. It can also help to pull hard on the filament while moving the gear by hand to give it some extra power.
Next step is probably to either remove the bowden tube or take the head apart.
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