I really don't know what happens when a wick is no longer useable. I suppose they eventually burn through, and crumble apart. I haven't been at it long enough to have it happen yet. I've replaced coils, and used the same wick, over and over. When I change flavors, I flush the tank out with Everclear in a syringe, and dry burn. Some of the Everclear wicks up, and when I dry burn, it cleans the wick. I don't get any left over taste from the Everclear, or the previous flavor.