All radiators in my daughters old dutch colonial in eastern U.S. have been working fine except for one room. I checked the pipe in the basement leading to the second floor when heat is on and the pipe is hot. When I checked the pipe attached to the radiator the pipe is cold. It did work once last year but not since. Could it be air in the lines? If it was the shut off valve we would at least get hot pipes feeding the source.

Do we have to change the pipes due to rust?

Can I take the shut off valve off the radiator and run a small snake down to clear the pipe or would that cause rust particles to block some other area?

Is there any additive that I cold put into the system to help this?

Need help, fixitpa