[Solved] PLA now giving trouble - diagnosis?  

RE: PLA now giving trouble - diagnosis?

When you switch from a higher temp filament (e.g., PETG) to a lower temp filament (e.g., PLA), it's possible for a bit of filament debris to get left behind in the hotend and nozzle. If this happens, you can get a partial clog from material that won't melt out. This can result in a number of extrusion problems depending on how bad the clog is. An easy way to clear partial clogs is a cold pull. You use a higher-temp material -- I like eSun cleaning filament -- to ensure everything is melted out.

1. Heat up the nozzle to a temp higher than your highest-temp filament (e.g., I use 265C for eSun cleaning filament).
2. Run some of the cleaning filament through the nozzle.
3. Stop and turn off the heaters and let the filament fully cool.

At this point, you've got the cleaning filament stuck in the hotend with any debris trapped within.

1. Loosen the extruder tension screws.
2. Start heating the nozzle again.
3. As the temp moves above 70C, start a slow, steady pull from above.
4. At some point, the filament should pull out from above, removing the partial clog.

Here's what a good cold pull result looks like:

More notes here and a Prusa knowledgebase article here for more info.