Re: Yet another hookah problem
It sound like the stem pieces have galled together. Stainless steel is good for resisting rust, but it is prone to thermal warpage and galling.
Applying heat can work, as long as it is applied unequally to both pieces. If they are heated together, they will expand together. The female threads need to be warmer to expand away from the male threads.
Freezing the stem and then pouring boiling water on the stem above the joint should work.
After you get it apart, check the threads for damage. If you see slivers of metal, or bent over threads, clean the threads with a thread file or tap/die. A light application of canola or mineral oil will help prevent it from happening again.