Candle tunneling occurs when only the center of the wax right around the wick melts and burns down but the wax on the sides does not. If candle tunneling occurs over time, you’ll end up with a ring of hard wax around the outside of the candle that will not melt when the candle is lit. Candle tunneling can occur in any candle, regardless of the quality or type of wax that is used.
You want to avoid candle tunneling because it reduces the overall burn time for the candle. It also makes it harder to light the wick as the candle continues to burn down. The best way to prevent candle tunneling is to allow a full melt pool during the first burn.
The first burn is critical to prevent candle tunneling. Candle wax has memory, and the first burn tends to set the radius of the melt. If you create a tunnel on the first burn, the next time you light the candle, it will melt the wax in the tunnel first, making it deeper and continuing to leave unmelted wax around the edges. That’s why it’s so important to completely melt the first layer of wax on the first burn before blowing out the candle.
You can fix a tunneled candle by wrapping a piece of aluminum foil around the edges and simply letting it burn. Make sure the foil hangs over the built-up wax areas but leave an opening in the center so the wick can still burn properly. After a couple of hours, the wax should melt and even out the surface.