Candle tunnelling?

What is Candle tunnelling?

When wax only melts a tiny circle around the wick during candle burning, rather than all the way across the candle, this is known as candle tunnelling. Eventually the wick may become impossible to light as the tunnel gets deeper.

To avoid tunnelling:

When lighting a candle, make sure you burn it for a sufficient amount of time to melt the wax all the way from the wick to the container's edge. In addition to releasing the maximum amount of fragrance, this will stop tunnelling in its tracks.