Indeed there are multiple causes, you'll have to look at the most likely causes and rule them out till you found your issue.
Have a look at the hot end part, if you remove the bowden on the printhead side, can you manually feed fillament with ease at normal temperatures ? in that case it's probably not the hot end causing it, do a few times "atomic" cleaning anyhow.
The other likely cause is the feeder, do you use the original manufacturer feeder ? this one can be dirty, filled with plastic particles, take it appart and clean it. Or better replace it by a improved printed feeder, most people use "roberts feeder" (I use my own derivative). These feeders are more "open" so you can easier clean them.
here's linkes to most of the info you need;
If you need other info best do an andvanced google search, most things you need are answered before in this forum. ( search in http://umforum.ultimaker.com/ )
Had this problem too, but there are actually too many things that can go wrong, like too much frition in the bowden tube, the teflon coupler, partially clogged nozzle,...
You might have to try multiple things to find your specific problem, I had to print about 1 hour at 260°C at a low speed and then everything was ok again.
Link to post
Share on other sites