TPU filament stuck in extruder
SOLVED. TLDR: I am reporting my experience with TPU filament being stuck in CORE ONE extruder. I fixed it by pulling it up and out through the idler (area?) using temperature, pliers, and the E-axis control.
Signs/Symptoms: Shortly after the print started the extruder started making a 'ratcheting' sound, like a fast clicking. The filament stopped coming out of the hot end and the print had small balls of TPU present all over the top layer.
Investigations: I stopped the print immediately on hearing the sound. I realised the filament must be stuck somewhere so I unlatched the idler to check the grooved roller (I am a beginner, go easy!) and noted the filament looked fine. Using the Prusa supplied pliers, I was able to pull down the filament easily which meant the obstruction must be below the grooved roller. When trying to 'unload' the filament I was met with the same sounds and although the filament could be felt to go into the extruder, it didn't come out, even with pulling on the filament manually, while the 'unloading' process was taking place. I used one of the supplied acupuncture needles to clean out the hot end with the temperature manually set to 260 (just in case some previous filament was in there) the needle pushed all the way in easily and came out clean.
Remedy: I was able to pull the filament out manually by doing the following; With the XY motors turned off. Temperature set to 260. The idler latch opened. I gripped the section of filament over the grooved rolled using the pliers, the other hand using the E-axis (which is the extruder filament advance/retract motor) to retract the filament while I pulled fairly hard. The filament thinned and I thought it was going to break, but thankfully it didn't and eventually the filament came free.
Things I learned: As a relative beginner, and with a pre-assembled machine, I found it difficult to understand what people were talking about on forums. I didn't know what an idler was, how to unlatch it, how the filament moved through the extruder, and for any information on the website about the noise I was hearing (I still don't know - grooved roller slipping on the filament?) Eventually, it was a post on this forum where someone discussed using the E-axis as a way to carefully guide the filament up and down. In hindsight, I should have taken some pictures to put here on my post but I was frustrated and tired and in a bit of a hurry to get it fixed.
RE: TPU filament stuck in extruder
Adjusting the temperature of my TPU up (200 to 220) solved the issue of filament getting stuck in the extruder. It wasn't, as I first suspected, an adjustment needed on the idler screws. I am a noob. I initially dropped my temperature down because I was getting stringing in my TPU prints. I have since solved that by slowing the print down ~30 mm/s and drying the filament down below 20%