I am assuming that it is the style of double boiler that has two pots?
Try immersing under water, hold the bottom pot down, and wiggle the top pot by the handles until it releases. You should feel the top pot sort of pop loose. (It is sometimes easier to have two people do this, just for the extra pair of hands.)
If the double boiler is made of metal, which I am assuming it is, you could try putting it somewhere cold so that the metal contracts and hopefully it will be enough to get them apart. Maybe your refrigerator, freezer or even outside will work.
Make sure the bottom pan heat has reached the top. Put ice and water in a pitcher and pour it in the top pan and make sure it is cold where the pan is stuck to the bottom and try to separate it immediately so that neither pan has a chance to cool off or warm up. Have someone hold the bottom tight and try rocking and turning the top one while pilling it up.
Spay some WD40 around the rim of the bottom potpot. Often what happens is a vaccum forms and it can be tough to break apart. The lubricant should make it easier to release the bond.
I am assuming that it is the style of double boiler that has two pots?
Try immersing under water, hold the bottom pot down, and wiggle the top pot by the handles until it releases. You should feel the top pot sort of pop loose. (It is sometimes easier to have two people do this, just for the extra pair of hands.)
If the double boiler is made of metal, which I am assuming it is, you could try putting it somewhere cold so that the metal contracts and hopefully it will be enough to get them apart. Maybe your refrigerator, freezer or even outside will work.
Try holding the bottom down in really hot water and put cold water in the top. The bottom may expand in the heat and the top contract in the cold.
Put cold water in the top pan and sit the bottom in hot water. The bottom should expand and top contract so they can separate.
Spay some WD40 around the rim of the bottom potpot. Often what happens is a vaccum forms and it can be tough to break apart. The lubricant should make it easier to release the bond.