I don't do candles but wax melts at a low temp can't you put it in the oven and start at like 200 degrees and move up the temp till it melts? pour it out and put it back in till it cools? just a thought

I suggest holding a metal rod and heating the rod carefully.
Using a cotton cloth is recommended.
Now melt the way in the middle to the depth you want.
Put a thick string or thread until the wax is molten.
remove the rod and there you Are.

The boiling water should work fine. If you use the stove and a pot for this, be sure to rig up a method to keep the jar suspended so as to not touch the bottom of the pan. Actually, I would further suggest filling the inside of the jar with water as well, to allow the glass to heat and expand in a much more uniform manor. The wax and the water in the jar shouldn't to too difficult to separate if you want to reuse it.

There are candle burners ( I think that's what they are called) out on the market now. Any candle or gift shop has them. You place a whole jar candle in one & turn it on, it melts the wax & puts the scent out into the room. I use them all the time in place of candles because you don't have to worry if you forget to turn it off, unlike forgetting to blow out a candle. This would work to melt your wax too so you could put a new wick in. Good luck