This pictured radiator is an example of what happens to a radiator when another radiator nearby has a failed steam trap, that has failed open and allows steam to blow into the return pipe. In the case of this particular radiator the next room over had a bad radiator trap. Now the interesting part is this radiator pictured is a good radiator. Its not heating. It however has nothing wrong with it. The bad radiator is the screaming hot radiator in the next room over. This can at times be difficult to communicate to someone. In their eyes the bad radiator is the cold radiator. See whats happening in the picture. The steam is trying to get into the radiator, but the air can't get out because the radiator trap is closed from reverse by steam that has blown through the next rooms radiators bad trap. The radiator is actually air locked and will remain cold. I call it steam locked since steam is on both sides of it. Interesting huh! The thermal picture is worth a thousand words in trying to explain this one.