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Old Cast Iron Radiators; Shut off Valve Question

Hi. I'm a homeowner not a pro but will share my experiences. I have a hot water system probably similar to yours. First, although I have not done it, breaking a valve could indeed be very bad news: Best case you will have to replace the valve at a future date. Worst case you will have several hundred gallons of water in your house. But to get to the point...

Yes, old rad valves often are worn out and will not close all the way. However if they will still turn they will often modulate the flow enough to balance temperatures. Now the trick - getting them to turn. There are several different kinds of valves. Some can be serviced without removing them and some cannot. The ones that have a cap with a (usually) square nut just under the stem packing nut can often be freed up by removing the handle, packing nut and packing, cap (by turning the square nut), then the internal valve parts, which will almost certainly require soaking in liquid wrench prior to removal. Clean everything and put it back together with a little automotive formed-in-place-gasket for the cap and new stem packing. I like to use a little plumbers heat proof grease on the valve parts but this may not be a good idea on a steam system where oil or grease in the boiler water can cause problems in steaming (I think).

Valves with no service cap must be removed from the radiator and the pipe to fix them, and if you're going to remove the valve from the pipes, I would replace the whole valve with a new one. They aren't that expensive compared to the hassle of getting one out and back in without leaks. If a valve does not have a service cap I personally consider it "pipe" and not a valve at all. It cannot reasonably be serviced, in my opinion.

By the way, did I mention that you must drain the system before you take anything apart? And know how to refill to the correct pressure and bleed the rads? Dan Holohans books are a great way to gain a decent understanding of how all this works.

My suggestion? Work on the valves in the summer, if you must.

Good luck, hope you get some responses from the pros.

Brian Macdonald


  • Msterspy
    Msterspy Member Posts: 1
    Cast Iron Radiator Shut off Valve Problem

    Hi All: I have an old heating system. It is a Forced Hot Water System with those old cast iron (about 30" tall) under every window. They are not recessed in the wall. Each of the upstairs radiators has a shutoff valve. It is my understanding that the valves only partially shut off the radaitor. Lately I notice that the tmeperature upstairs gets
    really hot and downstairs is cool. I tried shutting these valvles and most are hard to turn and I'm afraid I will brake one or cause leakage.
    Anyone have any experience with these radiator valvles? The last thing I need now is to break one of these in the middle of the winter.

  • well i take it you have monoflow (diverter system) in your house if you are regulating the heat in certain area's by throttling the valves.. how many zones or thermostats do you have in your house? that info would make it easier to explain how to drain, fill and bleed your zone without draining the entire system..
  • MsterSpy_2
    MsterSpy_2 Member Posts: 4

    I have two zones total. One zone is for a den which has baseboard radiatiors and the rest or the house is on one zone both first and second floor. I did detect slight dampness around one of the valvles that I have been turning. Guees I will leave it alone and keep an eye on it untile the summer. The valves I believe are serviceable.
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