Heat creep
My mk4 prints aproximately four layers and suddenly stops extruding filament and keeps up phantom printing. Since the printer passed the hot end tests, that implies the thermistor is working. The temperature readings square with the default pla and petg settings. There are no clogs. Filament purges. What is causing the heating issue and how do I solve it? The hot end temperature does not rise above the default filament values. The cooling fans are on when the temperature hits the threshold.
RE: Heat creep
Are you using the input shaping (MK4IS) printer profiles?
I found that at least on my PETG prints, I needed to increase the filament temperatures 5 or 10 degrees when printing with the STRUCTURE or SPEED print profiles. I was seeming very similar issues where the first few (solid) layers seemed to be mostly okay but would definitely fail right around the time it started printing infill.
RE: Heat creep
With the help of Prusa tech support, I discovered the source of my issue. The metal part of the thermistor separated from the wiring and was embedded in the heat block. I am awaiting a replacement from Prusa. It is going to be difficult removing the metal part of the thermister from the block. Even with the grub screw removed, it looks like the metal part of the thermister is cemented into the block.
RE: Heat creep
Glad to hear you got it worked out! Thermistor issues seem to be some of the trickier to work out. Things work but work inconsistently enough that it is difficult to troubleshoot.
Thank you for coming back to post the fix! A great example of a problem with a straightforward fix to help other users debug their printers.