I'm trying to find the reason why my bigger printer suddenly decided to constantly create blockages as high as the PTFE tube in the cooling block (so a little bit above the heatbreak).
It's an older V6 head. The discolouring on the heating block comes from the single time the nozzle came lose and PETG was pressed through the threads upwards, that was a year ago though. I didn't change anything, from one day to another it just decided that (for both PLA and PETG) it'll now stop working properly.
Waiting on a stronger cooling fan (strongest Sunon I could find, the one with 9000rpm). Other than that I'm just confused why this suddenly happens.
Swap nozzles? I've had issues in the past with partial clogs with petg in particular, at the least it'll remove a variable from your troubleshooting. Also echo what others have suggested and check out your filament path, make sure there's not somewhere else causing an issue. I feel like dusty filament could potentially contribute to clogs, if you're concerned with that there's designs out there for in line wipers that pass the filament through some soft sponge.
Do you have any resistance feeding the filament? I've had a few cases where either the filament kinda tangled due to slack and would still be able to feed but needed more force, bad enough it can actually wear the filament in the extruder and won't advance anymore. Extra friction from tight tubing, small radius bends, cardboard spools etc. can do that too. Check your settings for the tension spring as well, too tight can totally cause issues that will look like this and make you chase ghosts.
I run a fan like this one on mine (9.9 cfm/0.277 m^3^/min), the ones that push more air get loud quick just as a heads up, this one I was also looking at, is 12.2 cfm/0.342 m^3^/min but is 39 vs 31.4 dB, I did a bunch of fan upgrades last year for both better performance and less fan noise, these will be noticeable. Don't get heat blockages but do have some oozing I really need to get around to tuning.