"Filament stuck" errors every 15 seconds.
I recenlty assembled an MK4S kit. I printed several prints, including some big ones with no issues. I'd say about 20 or 25 prints over 3 or 4 weeks. I've printed in PETg, PLA and PLA+. I'm using the MMU3, but the kit came with the CHT nozzle altough it's not recommended. However, chat support told me the only difference is I should increase the wipe tower when printing in multimaterial.
However, a few days ago I started a print (single color), checked that first leyer was ok, and then left, when I came back the printer had only printed a few layers and was waiting on the "filament seems to be stuck" error screen. It was exactly the same gcode I have printed a few times already with absolutely no issues.
I did the unloading/loading routine and it resumed the print, but same thing happened again after a few minutes. Since then I've tried over 15 prints, and I've only been able to finish one, which I had to babysit through ~30 "filament stuck" errors. Every time the filament unloads and reloads with absolutely no problems, and print resumes for a while. Sometimes a few minutes, sometimes barely 5 seconds, before triggering the error again.
If I turn off the stuck detection, it's evident that it is not a false positive, as the filament eventually does get stuck and stops flowing altogether. However, if the detection is on, the uloading/loading occurs with no incidents every single time, and the purging always flows freely.
It USUALLY goes through the first solid layers, and the problem starts once it starts with the infill, altough it did get stuck once or twice on the first layer.
So far I've tried, with aboslutely no success:
-Loosening the idler tension screws
-Tightening the idler tension screws
-Loosening/tightening the MMU3 cover tension screws (although once the nextruder is engaged, the MMU3 sits idle)
-Switching to PETg, PLA, PLA+, trying different spools, including freshly opened ones.
-Cleaning the nozzle in place, using the needle that came with the kit, and also with another nozzle cleaning set.
-Taking the nozzle out and thoroughly cleaning it with the needle by heating it with a heat gun and also on the stove.
-Reslicing the piece with different profiles, both for the (CHT) high flow nozzle and the regular one. Also tried profiles for the MK4S without MMU3 (but then again, the only difference should be in the first loading part, since the print is in single material and the MMU3 sits idly).
-Different prints of various sizes and shapes.
-Increasing the nozzle temperature. The PLA+ I'm using is advertised to print in the 180-250 range, before this problem started I was printing at 215, I've now tried everything from 215 to 250). This seems to be the only thing to have a slight impact on performance, as it appears the problem is slighlty less frequent at higher temps).
-The "cold pullout" routine several times.
-"Manually" (settings/move extruder) extruding lots of filament, changing colors to check that no specks of previous color ever came out).
-Reducing (80%) and increasing (110%) the printing speed.
I'm about to order a new nozzle to be 100% that there's nothing stuck inside this one, but that will take a few days to arrive, and I don't have much hopes anyway, as purging works, first layers work, etc. so flow inside the nozzle really seems normal.
One thing that may be worth mentioning is that for that print that I did manage to finish after many many errors, the dimensional accuracy was hideous. The print surface quality is spotless (because the printer actually pauses on every error, and resumes flawlessly), but outside corners seems to "blob out", so a square looks more like if a castle had circular towers on each corner. This only happens on outside corners (presumably in insides corners it's hidden inside the piece). It gives the impression that some filament built-up pressure is releasing on sharp turns and it overextrudes. Again, I printed the same thing a few times before and it was a perfect square.
I'm absolutely at a loss. The printer is unusuable, every single print fails. I don't know what else to try. Any help is GREATLY appreciated.