Can't print anything, clicking and low extrusion
I had a similar issue after installing an E3D V6 using a Bowden extruder.

PLA needs a heat break that has a PTFE liner, since with all metal heat breaks, it's probable that the filament will reach glass transition temperature in the heat break and stop flowing properly.

Also, I had filament that was 1.86&nbsp;mm instead of 1.75&nbsp;mm, which caused it to bind inside the PTFE tube.

Before correcting these issues, I was able to temporarily fix the issue by doing a cold pull to unclog the extruder, and was able to print around 10&nbsp;cm in height of a 20x20x20&nbsp;mm cube.

To do a cold pull, heat your extruder between 80-100°C, and then pull out the filament. If successful, the tip of the filament will be shaped as the inside of the nozzle. If needed, heat the extruder to 200°C and manually push the filament to fill up the nozzle and heat brake, then let it cool down to the above temps and do the pull.