be careful pressing down too hard. i once had one that was stuck, and i just pushed harder. it finally moved, but very quickly, and i cut myself on the lip of the opening.
the hot water sounds like a good idea. you could soak it upside down in the hot water?
another option is to get a piece of wood and a hammer, and forcibly get it unstuck - be careful with this though, you don't want to bend any of the metal.