Do you actually see the extruder motor turning backward (retracting) at the start of the feed line?
I ask because not printing the first part of the purge line is normal. Filament naturally oozes out of the nozzle during preheat, so there won't be any filament coming out at first. The purge line is there to ensure it is properly primed before printing to correct for filament ooze during heatup.
I ask because not printing the first part of the purge line is normal. Filament naturally oozes out of the nozzle during preheat, so there won't be any filament coming out at first. The purge line is there to ensure it is properly primed before printing to correct for filament ooze during heatup.