slim8589

Had exactly the same problem with an Ultimaker 2+ and it was causing a lot of issues. However, it was relatively easy to fix in the end. Here is what I did. Remove the nozzle and with some fine wet and dry remove any residue from the flat end of the screw thread. Heat up the assembly without the nozzle and scrape off all the melted plastic. I then used a small flat bladed driver bit to scrape around the inside of the assembly where the nozzle would seat. Hold the assembly with pliers otherwise you'll burn your fingers!. I spent about 5 minutes gently removing any residue inside where the nozzle goes. Put it all back together while hot and bob's your uncle. No more issues. I suspect that when inserting the nozzle cold, plastic, which is on the end of the nozzle thread end and inside the assembly where the nozzle seats stops it from closing up brass to brass. Once heated the PLA that was in the way melts and a small gap is created between the nozzle inside end and where it seats allowing PLA to freely flow. Been running it for days since I did this with no issues.