Great post! I also recently assembled my UM1 and came here to find answers after melting my PEEK. I had sarted my first print (ultimaker man !) But I stopped after a short while when I noticed th print sliding sideways. Fixed a loose pulley.but left the temp at 210 or 220 for some time. Extruder quit working so I read about setting temp to 250 to clear a clogged nozzle. Fooled around reading wiki while nozzle was at temp and when I glanced again the nozzle was discolored and spewing burnt plastic droplets and some smoke. After cooling... PEEK plugged. Dismantled and hole through it plugged wit