All of the above Jinglepixie.
I usually will change a carto when one of the following happens:
1: Off taste: If Burnt taste then immediate trip to the garbage. If just off it gets cleaned.
2: Hard draw: Once again Clean and allow to dry completely, fill and test
vape, if nasty still, immediate trip to the rubbish.
3: Leaking out the battery post: Examine, dry up and re-install, if another leak occurs,
vape it till the flavor is gone and then immediate trip to the rubbish.
4: Does not fire at all: Unscrew, screw back in and try to fire, if nothing, immediate trip to the rubbish since it is clearly a dead stick.
Hope that is what you were looking for

Nate aka Darth Vapor