Fix a partial clog in the Prusa Mini+ hotend

August 08, 2021

Overview

I recently encountered my first issue with my Prusa Mini+. This printer was working wonderfully up to this point, and this ended up being a minor issue that was easily solved by consulting the online help articles available on Prusa’s website. The articles are written very well and include many pictures.

Issue and resolution

I was in the middle of a print when I started to hear clicking coming from the extruder. I quickly realized it was the extruder gear skipping over the filament, because it was unable to push it through the nozzle at the proper rate. As a result, the print became very stringy from under-extrusion. I first tried simply unloading/loading the filament, then starting another print. The printer would get through the first 4-5 layers without issue, but then the clicking would start. A Google search quickly brought me to this Prusa support article. Since I was able to load/unload the filament and there was some coming out of the nozzle, it was definitely a partial clog. I verified the idler screw was set correctly then proceeded to the cold pull. I didn’t see any material on the cold pull, and the clicking continued when I tried to print again. Next, I tried using the acupuncture needle to clear the nozzle. No luck there either. I began to do a little more digging and started to find several forum posts where people were having a lot of issues with the PTFE tube in the hotend. The issues seemed to all center around the tube not sealing well over time and filament building up around it. This would lead to, you guessed it, a partially clogged hotend. I followed the instructions in the “Disassembling the hotend” section of the article I linked to above. After pulling out the PTFE tube, I could see some trace amounts of filament around the edge of the heat break (not as much as the pictures). I was able to remove that material by doing a cold pull as described here without the PTFE tube installed. The material all came out on the first pull, but I did one additional pull just to be safe. When reassembling the hotend, I had to push the heater block up quite a bit further than it was initially to get a good seal on the PTFE tube. I reused the original PTFE tube, but I’m ordering some spares. Before moving on, be sure to check the extruder gears and clean them if necessary. Depending on how long it was grinding the filament, there may be some buildup.

After reassembly, the article jumps straight to performing a first layer calibration. In my case, I had to adjust the M.I.N.D.A/SuperPINDA sensor height due to how much I moved the heater block. I’m not sure why this step is left out of the clogged nozzle article. If you look at the article for replacing the hotend PTFE tube, it describes this process in step 14. After adjusting the sensor, I was able to proceed with the first layer calibration. I’ve now been printing for about 8 hours with no issues. I believe I can safely say the issue is resolved. I do believe I’ll see the issue again though based on what I read in several forums.

Possible upgrade

While I was researching all of this, I ran across several mentions of the same company that provides upgrade parts for 3D printers. The company is Bondtech, and you can find their upgrade parts for the Mini+ here. I’m strongly considering picking up the IFS Extruder and heat break. It’s interesting that Bondtech specifically mentions that their heat break and adjusted PTFE tube length prevents clogs between the PTFE tube and heat break. I am still enjoying my printer very much and the extensive help articles on Prusa’s site made fixing this issue fairly simple. I still wouldn’t hesitate to recommend this printer as an excellent starter setup.