Hi abobb, I just happened to see your post and am a bit late in this reply, but thought I'd go ahead anyway. You mentioned that there are two pipes on each radiator. Does one (the return) have a trap? If it does, there should not be a steam vent on the radiator. It is common for traps to fail, and once one does, it will generally cause the rest to fail. Once this happens, most times the "fix" would be to put air vents on the radiators. The system may work, but not efficienty. There is also a trap at the end of the steam line near the boiler which should be checked also. This vents the air from the steam lines. Also, your condensate pump must be operating. It's what pushes the condensate back to the boiler. Without it, your return lines will be flooded and most likely your system will be very noisy. If you don't think you can fix all of this by yourself, I'd call in an expert. Your system sounds like a vapor steam system, and if it is, it's the Cadillac of steam heating systems. Don't even think of converting it to hot water, as that would be an expensive option. The pipes are sized and pitched for steam. Converting to water would mean a lot of changes. One thing to consider is that a vapor steam system operates at less than 1 psi. Hot water uses a lot higher pressure, unless it's an open system, and most are not. This would mean that with the higher pressure, you'd most likely have leaks that were not apparent with the lower operating pressure of a vapor steam system. I noted that one of the posts gave a link to heatinghelp.com, which is an EXCELLENT resource for anyone who wants to learn how steam works. Once operating properly, you will love your steam heating system!