what happens if you don't top if off every week or so or you burn the flame for a long while as the fluid runs out, the wick develops carbon deposits (turns black) and will not catch a spark easily. you have to pull more wick out with pliers at that point and trim it off. you can only do this a couple of times before the wick in the casing no longer comes into contact with enough cotton to "wick" fluid for a proper ignition. At that point it's time to replace the wick. this is very easy and you can watch a you tube video to show you.