adjusting old radiator valves

[Heathcliff]

I have hot water heat with the old cast-iron radiators -- probably about 80 yrs old. The heat works fine but I would like to decrease the heat supply to a couple rooms upstairs that tend to be overheated. I have tried adjusting the valves on these radiators and, after scraping off the paint, applying penetrating oil, and loosening the big (7/8ths) nut that fits over the valve shaft, I still can't get them to turn more than a half-turn or so, not enough to have much impact on how hot the radiator gets. The valves are built into a 90-degree bend that connects the pipe coming out of the floor to the radiator. I could just wait until summer, then partly drain the system and take the valves apart, but I thought I would see if anyone has any tricks to try or if I am missing something. Thanks.

[Matt]

Oh yes, this is a very common issue, and probably 90% of people with hot water heating systems have run into it.

[New & Improved - N/F John]

I have steam heat, but the valve at the point of radiator connection does not control the rate at which the radiator heats up. You need to adjust that silvery do-dad on the other side of the radiator. If it isn't adjustable, you can buy adjustable versions at a good plumbing store. They cost about $30.

[Edwin Pawlowski]

Wait if you can. Have a new valve and fittings on hand if you cannot. Very good chance it will be worn and corroded to the point of needing replacing. This is not the type of job you tackle under pressure to complete as it will take longer than you ever anticipated. Old piping breaks, old valves break.