We have a 1927 Tudor, and a radiator on the third floor won't heat. Our system is steam with return piping (ie no release valves). The steam intake pipe coming up through the floor is also cold, telling me a clog is somewhere in the vertical pipe or the horizontal pipe in the basement. Can I take off the radiator, shut off all the others, and turn up the heat to try and unclog it with pressure? Are the any other tricks to try?