There can be many reasons for this. Either your temperature for the nozzle is too high, retractions are too long, or the front cooling fan is insufficiently cooling the heatsink. It may be all three but diagnose the machine for all three to be safe.
1. Lower the temperature of your nozzle by 5 degrees C increments
2. Lower retraction settings – for Bowden style printers lower it to 4mm and for direct drive style
printers lower it to 2mm
3. If the fan is not working, then the inside of the hotend would be clogged (heatcreep) causing the
filament to be stuck. Replace the fan.
There is another possible cause that I’ve seen pictures of.
The Boden tube is supposed to go all the way down and fit snuggly into the hot end. In the case I’m referring to, the Boden tube had backed out slightly. This caused the melted filament to spread out forming a bulge at the end that was larger than the Boden tube diameter making it impossible to remove the filament. The solution in that case is A) Heat the hot end to, say 10C above normal operating temperature. Wait a while for the filament to get molten, then pull it out while it’s hot. THEN B) Loosen the Boden tube nut and make sure the Boden tube is pushed all the way down into the hot end. Then tighten the nut again, being careful not to let the tube rise up until it’s secured.
I agree with Lego, Heat creep as its called it famous for locking up filament in the tube, I generally tighten down my fitting, back it out almost a turn, install my Bowden and clip on the fitting, then i tighten down the Bowden fitting and this locks it up good.
