It is possible that some of the burnt wick has fallen into the melted oil. We recommend keeping the wick trimmed to 1/4-inch and sometimes it’s not easy to do that without making a sooty mess. To help alleviate this problem we sell a wick trimmer with a built-in tray that catches any burnt wick so it will not fall back into the candle. So, stop using scissors or nail clippers or worse yet, your fingers and invest in a wick trimmer. So handy!