Why Is My Candle Tunnelling? How to Fix It and How to Prevent It
Tunnelling is when a candle burns straight down the middle and leaves a thick rim of hard wax clinging to the sides of the jar. It is caused, almost always, by cutting the very first burn short. The good news is that a tunnelled candle can usually be rescued, and preventing it in the first place takes nothing more than a little patience on day one.
What tunnelling actually is
When a candle burns, it does not burn the wick alone. The flame melts the wax immediately around it into a shallow pool, and that liquid wax is drawn up the wick and vaporised. The width of that pool is what determines how much of your candle you will actually get to use.
Wax has what candlemakers call a memory. On the first burn, the candle establishes how wide its melt pool is going to be, and on every burn afterwards it returns to roughly that same circle. If the first pool only reached halfway to the edge of the glass, the candle will keep burning that same narrow column for the rest of its life, sinking a tunnel down the centre while the outer wax stays solid and untouched.
The practical cost is significant. A badly tunnelled 200g candle can leave a third or more of the wax stuck to the sides, which is a third of the fragrance you paid for and never got to smell. Once the tunnel is deep enough, the flame also sits below the rim of wax, which starves it of oxygen, dims the light and reduces the scent throw further.
The single biggest cause: a rushed first burn
Most tunnelling is set in motion within an hour of a candle being lit for the very first time. You light it, admire it, then blow it out after forty minutes because you are heading out or going to bed. That forty minutes was not long enough for the wax to reach the glass, and the candle has now learned the wrong shape.
For a 200g candle in a standard jar, a full melt pool usually takes two to three hours. That is the commitment the first burn asks of you. Light your new candle at the start of an evening rather than the end of one, and let it run until the surface is liquid right the way across.
Three other causes worth ruling out
An untrimmed wick. A long wick produces a tall, flickering flame that burns hot and fast in a narrow column rather than spreading heat evenly across the surface. Trim to around 5mm before every burn.
A draught. Air movement pulls the flame to one side, so one edge of the wax melts while the opposite edge never gets warm. This produces a lopsided tunnel and usually a black mark up one side of the glass. Move the candle away from open windows, doorways, radiators and air vents.
A habit of short burns. Even after a good first burn, a candle that is only ever lit for thirty minutes at a time will gradually narrow its pool. Aim for a minimum of an hour and a half whenever you light it.
How to rescue a candle that has already tunnelled
If the tunnel is shallow, the foil method usually works. Take a strip of kitchen foil and wrap it around the top of the jar to form a collar, folding it inwards over the rim so it covers the unmelted wax but leaves a gap of a few centimetres open above the flame. The foil traps and reflects heat back down onto the hard wax at the edges. Light the candle and leave it for an hour to ninety minutes, checking on it regularly, and the rim should soften and level out. Remove the foil carefully, as it will be hot.
For a deeper tunnel, a hairdryer on a low heat setting held above the surface will melt the top layer of wax evenly. Let it cool and set flat before relighting. Never put a candle in an oven or microwave, and never add water to soften wax.
Once you have levelled the surface, treat the next burn as if it were the first: give it a full two to three hours so the candle relearns the correct melt pool.
Does the type of wax make a difference?
It does. Natural waxes such as soy and coconut have a lower melting point than paraffin and tend to form a wider pool more readily, which makes them somewhat more forgiving. Our candles are poured with a coconut and soy blend for exactly this reason, among others. But no wax is immune. A coconut soy candle whose first burn was cut short at forty minutes will tunnel just as stubbornly as any other.
The short version
Give the first burn two to three hours until the wax reaches the glass. Trim the wick to 5mm before every use. Keep the candle out of draughts, burn it for at least ninety minutes at a time and no more than four hours, and stop when about 10mm of wax remains. Do that, and tunnelling simply will not happen.
