Cold, two-pipe steam radiator next to outer wall. Trap new in 2009, wet condensate in trap and draining. Trap is open.
Steam enters supply valve but doesn't seem to be migrating into radiator. I even loosened the trap cover just enough to allow air to escape when steam came up; I got a 'hisss' but steam did not fill the radiator. First section gets luke-warm.
Supply valve says open. Any ideas before I detach the supply valve to inspect?
While I was tinkering around, I tightened a hex nut that had come loose over time on top of the supply valve. I didn't think anything of it, cleaned up and left the house for a while. When I came home, the radiator was hot! The nut must have pulled up the disk. (I'm no plumber, but that's my theory).