yes, it is the non-melted ABS inside nozzle that blocking it. This ABS doesn't stick on the nozzle and can't seem to be melted all the way. I left it preheated to 250 degree for a whole 15 minute but still can't seem to melt all of the ABS inside the nozzle that connects to the end of the filament inside of the nozzle. This ABS is bought from flashforge-usa