It’s not necessarily the filament that is contaminated. PLA is known for clogging up nozzles. Try ‘seasoning’ the hotend with canola oil. I don’t know if the temp that is set, is the actual temp; (NTC might be off, i don’t have got a working IR gun right now) I’m now down to ~175 degrees on my vertex with PLA for the best results, without the PLA ‘burning’.
For PLA i print this 15x15x80mm 1 perimeter cube with a 3mm skirt to test the temperature of the filament; filament differs from manufacturer to manufacturer, colour to colour.
This is the temperature for the height of this ‘tower’ (m104 sets the temperature of the extruder the number behind S defines the temperature in degree c)
8mm M104 S200
16mm M104 S195
24mm M104 S190
32mm M104 S187
40mm M104 S184
48mm M104 S181
56mm M104 S178
64mm M104 S174
72mm M104 S172
For PLA i’m now down to 177 degrees first layer at 185 . (again, don’t know if the NTC in the nozzle is reading the correct values)
Here is the gcode for that test we.tl/YQus3jK6Gf (also running it on my K8400)
I’m on 151.9 steps per mm for the extruder, vs the 200 steps as defined in the software.