PLA from the top of the hotend My custom printer is affected by a strange problem. After 30/40 min printing without any problem, PLA starts blobbing from the top of the hotend.



What does it means? Where to start checking?

It is possible that there is a little space between nozzle screw and transition screw inside the hotend?
This is a typical sign, that your hotend wasn't tightened properly. Carefully heat it up and remove all the plastic you can while removing the heatbreak - that's what you call transition screw.

After cleaning, screw in the heatbreak and the nozzle. The nozzle should butt agains the heatbreak, but have at least 2 threads to the heating block. Reassamble the full hotend now by adding the coolend.

Finally heat the hotend on the full assembly to about 240 °C and tighten the nozzle against the heatbreak again. This is called hot-tightening. You can add the PTFE liner after the hot tightening.