[Alvy]

Is yours damaged or are you changing to a stack or something? As stated they are a pain but with a lot of patience you can get them out with soaking every day for a week or so with penetrating oil and I got some of mine with constant down pressure with a pipe wrench and smacking different directions lightly with a rubber hammer. I took an old one I had laying around and cut some flutes in it and used as a sort of tap afterwards to clean out the threads. (Got that from someone on here can't remember but it worked well).i would imagine worse case scenario would be to cut it off leaving a little protruding and cut slits inside it and use a chisel to break the pieces out but you have to be super careful of the threads. Those tjings grow together sometimes because of various reasons.

Also, what were you heating? If you heat the pipe it will expand and you don't want that. Were you heating the head around where the pipe goes in?