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.

enter image description here

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?

  • $\begingroup$ I've had the same problem, and the answer you selected fixed it. $\endgroup$
    – cmm
    Mar 1, 2020 at 21:50

1 Answer 1


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.


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