This thread was all from fall 2017, but in case anyone happens upon it, I figure I'll add my story. I was using dried PVA but got the same problem. I kept trying hot and cold pulls and reaming up the nozzle with a 0.4mm drill. Lightly using a 2.5mm drill from the top and the small drill from the bottom had me stymied how there was still a clog. I encountered no resistance on the drill through the extruder but could never print. I ended up disassembling the printcore (while waiting for a replacement printcore to arrive) and soaked the nozzle, by itself, in boiling water. After awhile, the small drill through the extruder was able to push the clog up and out of the extruder. My guess is that every time I tried reaming the nozzle previously, it was dislodging the clog up further into the assembly, only to be pushed back into being a clog when trying to print again. Of course, it's a very delicate thing as the section of barrel connecting the heater block to the heat sink is extremely thin, but it all worked, and I'd like to say that that printcore is working better than most of mine that are a few years old.