"Does the exterior of the pipe really get that hot? I don't know because I keep a radiator cover over the whole assembly, but I doubt I have a 250 degree exposed pipe in my living room" Steam is 212 degrees at zero #'s pressure. And by not stating how many floors there are between the boiler and your top floor condo I could only assume its greater then zero. As steam pressure increases so does its temperature, considerably. Why ask a question then question the answer? OK, you'll need something that will withstand at least 212 degrees. Is that better?

Brewbeer -- my problem is that while i can cut back and go to the next joint in line, whats to say that this one will come out. Also, the joint i was planning on, the one I can't get unstuck is a tee, with the master bedroom radiator on the tee. I will have to redo the tee if I cut back to the previous one and that runs through the floor currently -- ugh. There is an exposed coupling below that I can get at, it is just a coupling, two female ends connecting a run of pipe -- when you say break it off do you literally just whack it with a hammer or sledge until it breaks? I know that sounds kind of ignorant, but I have never been unable to get the pipe/joint turning before. kframe -- You are inadvertantly commending yourself and the other fine folks here on the gardenweb as I have trouble shooted and fixed my steam system (and lots of other things in my old house) with your guys help over the past three years. The main vents were a particularly helpful tip. I don't think its the mains getting clogged as the two radiators below the one to be removed on the riser work great until the one I'm removing gets consistently involved. My half baked theory is that that the length of the main plus the riser then going into a room that is consistently cold causes the steam to condensate by the time it hits the third floor leading to the whole riser backing up and shutting down. I tried to throttle down on the lower and closer radiators and opening the third floor all the way and all that happened was the whole house was cold. I have gone so far as to run the system with everything down low and the radiator that I am dealing with with the valve off and the the radiator still does not get warm, boiler shuts off before it gets hot. If i cut into the floor, i likely can get a reciprocating saw in there -- what can I do with it other than ritual hari kari before my 8 months pregnant wife finds out she cannot turn on the heat.

lazypup's in the ballpark but I think his long discourse on cavitation is more tailored to an extreme version you'd see in a hot water system. Cavitation occurs at a microscopic level. It happens at points in the pump volute and on the impeller where low pressure occurs (the trailing edge of the impeller is the best example). If the suction head required by the pump to operate is greater than what's available due to suction line throttling or friction losses, the low pressure becomes low enough to cause water to vaporize. It's technically "steam" but not like you think b/c it can happen even at room temperature. This can be exacerbated by pumping a hot fluid b/c it has a higher vapor pressure (i.e. it 'boils' easier). Your pump can be sitting there pumping water pretty much normally and still be cavitating. Lazypup's description makes it sound like you suddenly get a pump full of steam, but that's not the case. The bubbles that are formed by cavitation immediately collapse back on themselves and that's what causes the pump's parts to erode, since the bubbles occur at surfaces in the pump. It sounds like you're pumping marbles. Lazypup's description sounds more like a pump that's air binding. For hot water, it can be an extreme version of cavitation. But what he describes sounds more to me like a situation where the pump is depending on the pumped fluid for some of its lubrication/cooling. If the fluid isn't there, then the pump can quickly overheat.

I realize that this is an old thread but I want to respond for anyone with a similar problem in the future. I am amazed that someone would tell you to hire a licensed plumber for such an incredibly easy job. Come on, folks! Have we become so helpless? When I read the question, I assumed it was about copper or galvanized pipe which would be very easy to fix too but then I saw it's PVC pipe. Nothing could be easier to fix and I have no idea why the person asking the question thinks he cannot remove the elbow. Of course you can remove it! You can simply cut it out with a hacksaw and put in a new elbow. You can extend the pipe that is cut off easily with just a union and a piece of PVC. Working with PVC is so incredibly easy that I am baffled about why the question was even asked. A proper repair would take about ten minutes and cost a couple dollars. I never cease to be amazed by how helpless people are becoming. This is pretty sad.