Tunnelling is the most common and most frustrating problem in candle making. You light your candle, burn it for an hour or two, and blow it out — only to find a narrow well of melted wax around the wick while the rest of the surface stays solid. Over repeated burns, the tunnel gets deeper and the usable wax shrinks until the wick drowns in a pool of liquid wax and the candle is effectively finished with half its wax still stuck to the sides of the jar.
The good news is that tunnelling is almost always fixable, and once you understand why it happens, it is easy to prevent in future candles.
Why Candles Tunnel
Tunnelling happens when the melt pool — the circle of liquid wax that forms around the flame — does not reach the full diameter of the container. Soy wax has a “memory” effect: wherever the melt pool reaches on the first burn sets the pattern for every burn that follows. If your first burn only melts a 4cm circle in an 8cm jar, the candle will continue to melt in that same 4cm pattern until the wick is gone.
There are two main causes. The first is an undersized wick — one that simply does not generate enough heat to melt the full surface. The second is an insufficient first burn — blowing out the candle before the melt pool has had time to reach the edges.
How to Fix a Tunnelling Candle
The Foil Method
This is the most reliable rescue technique. Tear off a piece of aluminium foil large enough to cover the top of the jar, then fold it in half for durability. Place it over the candle opening, leaving a small hole (about 2cm) in the centre for the flame to breathe. Light the candle and leave it for 2-3 hours.
The foil traps heat above the candle, raising the temperature inside the jar enough to melt the wax walls. Once the surface is fully liquid and level, remove the foil carefully (it will be hot) and let the candle burn normally. The reset melt pool should hold on subsequent burns.
The Hair Dryer Method
If you do not want to burn the candle, you can use a hair dryer on its highest heat setting to melt the wax surface evenly. Hold the dryer 10-15cm above the candle and move it in slow circles until the entire surface is liquid. This levels the wax and resets the surface, though it does not address the underlying wick size issue — the candle may tunnel again on the next burn cycle.
The Oven Method (For Severe Tunnelling)
For candles with deep tunnels where the wick is too far down to light, place the jar on a baking tray in an oven set to the lowest temperature (typically 50-60 degrees Celsius). The wax will slowly melt and level out over 15-20 minutes. Remove carefully, let it resolidify at room temperature, and trim the wick before relighting.
How to Prevent Tunnelling in Your Candles
Prevention is easier than fixing. These three habits will eliminate tunnelling in the vast majority of cases.
Choose the right wick size. This is the single biggest factor. Your wick needs to generate enough heat to create a full melt pool across the container diameter within 2-3 hours. If you are consistently getting tunnelling, your wick is too small. Read our wick sizing guide for specific recommendations by container size.
Get the first burn right. The first time you light a new candle, plan to keep it burning until the melt pool reaches the edges of the container. For a typical 8cm jar, this takes 2-4 hours. Never blow out a candle on its first burn before the pool is complete — the wax memory will lock in the smaller diameter.
Trim the wick before every burn. A wick that is too long produces a tall, flickering flame that generates inconsistent heat. Trim to 5-6mm before lighting, which creates a stable flame that spreads heat evenly across the wax surface. A wick trimmer makes this much easier than scissors, especially in deep jars.
When Tunnelling Means Bigger Problems
If you are making candles to sell and getting consistent tunnelling across a batch, the issue is almost certainly wick sizing. No amount of customer instructions about first burns will compensate for an undersized wick. Run proper burn tests with multiple wick sizes before committing to production batches.
Occasionally, tunnelling is caused by factors beyond wick size. Candles placed in draughty locations will tunnel because moving air disrupts the melt pool. Candles with very high fragrance loads can clog wicks, reducing their heat output. And some container shapes — particularly tall, narrow vessels — are inherently more prone to tunnelling because the heat has further to travel to reach the walls.
If you are a beginner still getting to grips with the basics, our complete candle making guide covers the fundamental technique step by step. Getting the process right from the start prevents most of these issues from ever occurring.
