Check For Clogs In Your Cold End (Heatsink):

Occurs when excess Filament or PTFE tubing melts and clogs the passage in the heat sink.
Caused by insufficient or malfunctioning Cooling Fans in the Cold zone
Can also be caused by Heat Creep, where the Hot zone melts small amounts of filament or PTFE tube overtime, clogging the bottom of Coldend.
May be difficult to catch - changing the Hotend or Nozzle will not fix the Coldend Clog

Finding Coldend Clogs:

1. Try pulling your PTFE Tube out of the Extruder. You may have a Coldend Clog if the end is stuck or deformed (Make sure to first remove any clips or fasteners holding the tube in place)
2. Remove the Hotend and Nozzle and Look to see if the Coldend passage is blocked, any clogs should be directly visible

Fix Coldend Clogs:

Pre-heat your Nozzle to the temperature of the filament you want to perform a cold pull with
Pull the PTFE Tube out of the Cold end and push your filament through to remove any excess filament or debris in the passage
Continue to push the filament so it oozes through the Nozzle - Start to cool down the nozzle while continuing to apply pressure
Once the nozzle temperature drops down to ~ 60°C, pull the entire filament out: Any previous filament debris should now be melted into the cold pull filament and appear in the shape of the inside of your Nozzle
Look for any deformities on your PTFE tube (Narrowing or partially clogged sections) and Trim them off using a sharp knife.
Insert the trimmed PTFE tube back in, make sure there are no unclogs and the inserted end is flat
If necessary, replace Heatsinks that can't be uncloged or PTFE tubes that are severly damaged

Symptom