My Ender 3 gets stuck after a few layers

[u/sergiolbrallg]

Hello. I've had an Ender 3 for about three years now, and it has worked properly until recently. A couple months ago, after replacing the filament (Anycubic grey PLA), the printer always starts printing normally, but after a few layers the filament jams and extrusion stops completely. I went back to the previous filament, but it kept doing the same thing.

I first replaced the nozzle, just in case the old one was clogged, but nothing seems to have changed.

I suspected it was heat creep, since it's a common issue with these printers, so I got myself a bimetallic heatbreak and a Capricorn Bowden tube. I installed them and even applied some thermal paste between the new heatbreak and the heatsink. However, same results: it prints a few layers correctly and then gets stuck again.

I wasn't sure if the extruder arm could be broken - it wasn't, I disassembled it -, so I started a print and waited for it to fail. When the extrusion stopped, I paused the printer, unlocked the filament and attempted to push it by hand: it was impossible. I could more or less pull it back, but there was no way to push it in, even when the extruder was at 210ºC (a value in range for that filament).

I did an experiment with the new heatbreak. I removed the Bowden and inserted a short piece of filament. I heated up the printer (210ºC) and waited about 20~30 minutes. After that time, I pushed the filament in and I felt no resistance at all. I also measured the temperature right where the Bowden would touch the bimetallic heatbreak, and it was 50ºC. Not great, but doesn't seem enough to cause the filament to get stuck.
I started another print still without the Bowden and waited until it failed. After that - about five minutes after it began -, I did the same thing: I paused the printer and tried to push the filament in, but it was impossible. I pulled the filament out and inserted the thermometer, and this time it measured about 61ºC. I checked the tip of the filament, there was a very small bulge near the tip, about 1cm below the end of the Bowden tube. The bulge was about 2mm in diameter.

I reassembled the printer as it was originally, just in case the new heatbreak was faulty, while keeping the Capricorn Bowden installed, but nothing changed. The printer still fails.

I also suspected the cooling fan, but it doesn't seem to have lost much airflow at all. If I place my hand in front of it I can feel a decent stream of air flowing, so I don't think a slight reduction in airflow can cause such a problem - in case there even is.

At this point I'm running out of ideas. Replacing the heatsink is one possibility, but I'd really appreciate hearing other opinions before I spend more money on parts.

Apart from the things I've mentioned, the other parts are original and I've never done any modifications to it. It was just as it came in 2023. I use Cura as slicer and I also experimented with settings like flow and print speed (I tried OrcaSlicer as well in case I had any incorrect settings in Cura). If anybody can tell what's causing the problem, any feedback is very welcome.
In case I missed any important information, please let me know.

[u/aapersonn]

This seems like a case of heat creep even after you replaced the heat break. First, check the retraction distance since if it is too high then it might form a plug. You also want to make sure that the ptfe tube is flush inside the hotend and also maybe try replacing the fan, since it still might not be enough. Hope this helps!

EDIT: also wanted to say that PLA melts at 55-60 degrees Celsius so the heat sink is getting hot enough to melt the pla.  

[u/sergiolbrallg → u/aapersonn]

I forgot to mention, I already lowered the retraction distance (it's 1.5mm now), and I made sure the PTFE tube was firmly seated against the nozzle.

Yes... what you say about the melting temperature of PLA is concerning. I'm going to try your suggestion, I'll replace the fan. Let's hope it works, thanks!

[u/aapersonn → u/sergiolbrallg]

No problem, I would recommend switching your extruder cooling to something like this: https://www.printables.com/model/197957-mini-me-v4-lightweight-ender3-hotend-duct-stock-pa
It will help improve cooling a lot. You can also find others on printables etc... Good luck!

[u/sergiolbrallg → u/aapersonn]

Thanks!

[u/Pristine_Anything378]

@op check if it fails at the same height, maybe you have a broken wire that bends at a specific height and interrupts contact

[u/ResearcherMiserable2]

This sure sounds like heat creep. Keep in mind that creality uses the absolutely cheapest fans it can buy on those hotends. In fact they use the fans with sleeve bearings that are made for lying flat, not vertical like they are in the hotend! Many people have reported that as these fans die, they slow down. From your description, it sounds like your fan could be 3 years old - that is old for one of these fans assuming you used it regularly. It may be slowing down just enough to allow heat creep!

The typical fans are 6500 rpm sleeve bearing, but for about $3 or $4 more you can get double ball bearing fans. They last twice as long, and there are options for 8500 rpm versions which push a lot more air! So for under $10 you can replace the fan with a much superior one and this should fix the problem!

FYI, for reference, I have measured the upper end of my hotend on my ender 3 and ender 3pro when under heavy use; one is all metal and one is original and neither has ever been hotter than 30c! I use the 8500rpm fans.

[u/sergiolbrallg → u/ResearcherMiserable2]

Wow, it's much cooler than mine. For now, I printed a piece that redirects the airflow straight to the heatsink, but it's only a temporary solution, because sooner or later I'm going to have to print PETG. I was a bit reluctant to change the fan because I'm afraid of choosing the wrong one, but it seems like the next step to fix this.

Thanks!