I was running off some 2 color lids for my Gridfinity Latching Bins, and had two print failures in a row. Both of them were clogs inside the extruder, and I think both were related to heat creep. The reason for that suspicion is that my printer enclosure duct fan had a failed switch (which I have since replaced), but that meant that I ran the prints with no airflow through the enclosure. The gray filament which clogged is High Speed PLA as well, which I think may be part of the issue (since PLA is the most likely to have heat creep issues being a lower temp material). The clogs are due to the filament softening inside the extruder, where instead of gripping the filament, the gears smoosh it, and deform it to the point that a bulge forms, which can get stuck. The first clog I just cleared, but the second time it happened, I decided to swap some components out. I also found that the hotend was slightly bent, though not so much I'd normally swap it, but in this case I did (to rule it out as the cause). I also swapped the cutter and gears, since they were looking a bit worn.
The problem with a clog inside the extruder is that it will not pull out, and will not push in, so the only way to remove it is to remove the hotend or the extruder if that does not work. The other problem is that a clog like this makes disconnecting the bowen tubes very hard. So it helps to manually push about 1cm of filament in from the AMS end, which can get just enough slack to open one bowden coupler and clip the filament inside to release the tension in the tube. From there, the clog may be removed from below the extruder (with the hotend removed), otherwise the extruder will have to come out. Having a small cordless screwdriver and some hex bits for this is really handy for working on the extruder. The only part which is a bit sketchy is removing the wires for everything. The extruder wires originally had some glue on the connector, but even without it, care has to be taken when removing and re-installing the wires, since it is easy to misalign the connectors. To pull the extruder, the stop screw on the cutter arm needs to be backed out to free the cutter, then all three of the hotend connectors need to be removed, along with the extruder connector (four total). Then there are 3 screws that need to be removed to free the extruder from the toolhead.
The problem with a clog inside the extruder is that it will not pull out, and will not push in, so the only way to remove it is to remove the hotend or the extruder if that does not work. The other problem is that a clog like this makes disconnecting the bowen tubes very hard. So it helps to manually push about 1cm of filament in from the AMS end, which can get just enough slack to open one bowden coupler and clip the filament inside to release the tension in the tube. From there, the clog may be removed from below the extruder (with the hotend removed), otherwise the extruder will have to come out. Having a small cordless screwdriver and some hex bits for this is really handy for working on the extruder. The only part which is a bit sketchy is removing the wires for everything. The extruder wires originally had some glue on the connector, but even without it, care has to be taken when removing and re-installing the wires, since it is easy to misalign the connectors. To pull the extruder, the stop screw on the cutter arm needs to be backed out to free the cutter, then all three of the hotend connectors need to be removed, along with the extruder connector (four total). Then there are 3 screws that need to be removed to free the extruder from the toolhead.
Once removed, there are a few more screws which hold the cover on. Once those are removed, the screw which tensions the spring has to be backed off enough to loosen the idler (but note how tight it is before, since it has to be put back the same way). Then the filament can be pushed through and the clog cut off, and the filament pulled or pushed through the until it's clear. At that point, the yellow gear can be removed, though it will be tight still, and may require some work to remove.
When I compared the yellow gear to a spare I had, I found that it was a bit worn, so I swapped it out. The new gear also has a helical tooth pattern between the smaller gear and the idler, which should help with backlash. These are not very expensive, and will be a wear item, so it is a good idea (especially now) to keep a spare around. The gear I removed will be kept as the new backup, until I get some more spares, since it is not horribly worn, but it is a bit worn. Worn extruder gears will cause backlash in the extruder, and poor surface quality with inconsistent retractions - I doubt that was much of a problem with mine though.
I gave the extruder a good cleaning with alcohol and swabs, and then put a very small drop of oil on each of the bearings and steel rods in the extruder. Then the gear and hotend were swapped, I also replaced the cutter and re-assembled everything. I've run another print using the same high speed gray PLA, without a problem (though it was a single color print). I suspect the problem is solved, and really, I could have probably gotten by with just clearing the clog and cleaning things up, but it was a good time to overhaul things, with it all apart. The real fix in this case, was likely lowering the temp inside the enclosure to avoid the softening of the filament inside the extruder. Fixing the enclosure exhaust fan was a bigger job, but allowed me to re-print part of the enclosure back shell, so I could use a new 2.5" hose fitting, and a larger switch for the vent fan.
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