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After printing some parts in TPU, I encountered continuous clogging after returning to PLA. Not right out of the bat, but after about an hour or such, all prints I started since the swap back clog after about an hour. I use an Ender-3, Bowden Style, and print my PLA generally at 200 °C. The TPU had been listed as 220-240 °C on the roll, so I printed at 230 °C.

How can I regain normal printing behavior?!

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  • $\begingroup$ I first commented on your answer about lack of seeking additional information before realizing this was a self-answer question. Can you elaborate with what temperatures you're using for each material, and whether you have a PTFE-lined or all-metal hotend? $\endgroup$ Jul 2 at 16:15

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The problem is the dissimilar printing temperatures:

  • TPU is printed at around ${230\ °\text C}$
  • PLA is printed at around ${200\ °\text C}$

As a result, when the PLA is molten and well printable already, residue of TPU in the hotend is at an awkward spot: it is molten enough to seep down along the filament path with molten PLA, but it is not soft enough to get easily extruded from the nozzle. This is what leads to clogging.

To fix the clogging, I took the following steps:

  • Swap the nozzle to reduce the residue still in the machine
  • Do a cold-pull with the PLA, taking away a quite good chunk of the residue that still might remain in the heatbreak.
  • Finally, do a purge print at an elevated temperature. For me, about ${215\ °\text C}$ did work to get the last traces of residue from the heartbreak out.-

There you go! One restored printing behavior!

Technically, the nozzle swap and cold pull were overkill, but reduced the amount of TPU that needed to be purged out of the nozzle.

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  • $\begingroup$ This probably works (presumably it did for you), but switching materials should be a lot easier than this. $\endgroup$ Jul 2 at 16:16
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    $\begingroup$ Why not just clean the nozzle at TPU temperature and purge some PLA through? Works for me $\endgroup$
    – Kilisi
    Jul 3 at 12:35
  • $\begingroup$ @Kilisi possibly swapping the nozzle was overkill... $\endgroup$
    – Trish
    Jul 3 at 12:39
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    $\begingroup$ Perhaps, but it's a fullproof solution, so worth mentioning $\endgroup$
    – Kilisi
    Jul 3 at 12:45

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