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I have a hot water (or steam?) radiator that leaks water unless it's completely open or closed.

The side has a valve that can be turned to open or shut the connecting pipe. The other side has a steam vent.

If I fully open the valve, everything works properly, but it gives off way too much heat.

If I open the valve just a tiny bit, it's still too hot, but bearable. However, it will leak from the steam vent (enough to pool up before it can evaporate).

I told the super of my apartment about it, hoping it could be fixed, but he said just to leave it wide open or shut it off.

I've determined I have a single pipe, steam radiator, with a steam vent on the side opposite the heat pipe.

I read bleeding could help, but my radiator does not have a bleed valve, so I turned it off and removed the steam vent instead.

Some water seeped out. Then I turned it on, and lots of water shot out. Convinced this was a steam radiator, I let this continue until it seemed less like warm water and more like scalding hot steam instantly turning to water. When that happened I turn it off.

bled water
About two and a half jars worth of water shot out. Quarter for scale.

I then replaced steam valve and turned the radiator back on, and I'm now waiting to see if it will still leak.

However, this did not help at all.

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3 Answers

up vote 4 down vote accepted

I'm afraid your super is right. The supply valve must either be fully open or fully closed. If it is partially open, condensate cannot properly drain back to the boiler. It will collect in your radiator instead. How much heat is put out is regulated by the size of the vent valve. If the boiler works by central control, meaning the steam goes on and off for the whole building to regulate heat, you can regulate the heat put out by the radiator by getting a thermostatically controlled one pipe steam radiator vent valve, or simply getting a smaller vent valve.

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Ah, right...I can picture what's happening now. –  Louis Nov 4 '12 at 2:47
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This is pretty common with globe valves because the plug does not completely seal unless it is fully open or fully closed. If there is a packing nut you can try tightening it to see if this stops the leak but otherwise your best bet is to replace the valve with a ball valve (turns 90 degrees to fully open or close) as these are more reliable and don't exhibit this problem.

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Okay, I'll see if I can replace it with a ball value. I was looking at the diagram and I can see how it's not completely sealed unless fully open or closed. But I don't understand why the water comes out from the vent on the other side of the radiator. In the diagram, it looks like the water should come out of the valve stem. –  Louis Nov 3 '12 at 16:03
    
Sorry but when I first read the question I didn't grasp that it was leaking from a different valve - this answer probably won't help. –  Steven Nov 3 '12 at 16:39
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I've determined I have a single pipe, steam radiator, with a steam vent on the side opposite the heat pipe.

In this case, the valve is a shut-off only valve, not a system to regulate with. Partially closing it will limit the removal of condensate and then you'll have built-up water. It should always be left open.

If I fully open the valve, everything works properly, but it gives off way too much heat.

Abou the valve and regulation: regulation is on the other side. The "steam vent" you mentioned on the other side of the radiator is actually an air vent. This is what controls the proportionate amount of steam entering your radiator from the system, and thus how much heat your radiator gives off. You didn't mention an adjustment knob, so what you have is a fixed-size regulator that is too large.

New adjustable vents can be had for ~$10. Replace your current vent with one of these and adjust it as needed until the radiator keeps you comfortable.

I read bleeding could help, but my radiator does not have a bleed valve, so I turned it off and removed the steam vent instead.

This is a term related to hot water heaters. Over time, they build up air in the top of the radiator that needs to be let out until water flows again. A steam radiator will only provide heat if it properly venting air ("bleeding") and that is automatically done through the air vent which allows flow until steam hits it.

... I removed the steam vent instead. Some water seeped out. Then I turned it on, and lots of water shot out. Convinced this was a steam radiator, I let this continue until it seemed less like warm water and more like scalding hot steam instantly turning to water. When that happened I turn it off.

Don't do that. Scalding hot steam scalds.

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