Why don't the upstairs cast iron radiator heaters work?

Answer 1

Most often because they become air/water-locked. A cast iron radiator system works by sending steam (which naturally rises) up from the lower level into each radiator. When the steam heats the cast iron it loses enough heat so that it cools back to a water (liquid) state. When this happens, the water must flow back to the burner all by itself, propelled ONLY BY GRAVITY. So if at any point in the loop ANY length of pipe has sagged so that it is not downhill enough to allow the water to drain, the system will become locked at that point and no steam will pass by, thus cutting off heat to all radiators beyond the blockage. The most common fix for this is putting shims underneath the feet of the radiator on the opposite side of the pipe only, thus angling the radiator down for full drainage. Many times people will cause the issue themselves by putting a floor or tile underneath the radiator, inadvertently removing the angle. Other times, the natural sagging of the house removes the angle put in when the system was originally installed. So, your best bet is to 1.) Shim all non-working radiators downward toward the pipe, 2.) Drain the whole system (from the spigot at the base of the burner) of all water (and air), and 3.) re-fill the burner with water to the appropriate water pressure. Replacing the steam valves on each non-working radiator is a good idea as well.