Trouble Bleeding Radiators


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Old 10-12-07, 07:13 PM
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Question Trouble Bleeding Radiators

This is my first winter living in a house with hot water radiators and I'm having a little difficulty. . .

The problem is I have two radiators on the third floor that when I bleed them, air comes out for a while, 10 seconds or so, then gradually stops and no water comes out. I've confirmed that the control valves on each radiator are open. As I'm bleeding those two radiators, i can hear water gurgling inside. I've bled these several times when the circulator pump is running and also when it is off. Each time I do it more air comes out, but never any water.

When the system is running one of the two problem radiators only gets hot on the bottom and stays cold at the top. The other radiator actually gets appreciably warm at the top, but certainly not as hot as the bottom.

I have a two pipe system and there is only one heating zone in the entire house. The water pressure on the boiler reads 15 psi.

The only thing I can think of is that the water pressure really isn't 15 psi and I don't have enough pressure to get water into the radiators on the third floor. 15 psi works out to about 34 feet of water which should be enough to get it to the third floor. Could that be it?

I'm not sure if as I'm bleeding the radiators new water is being let into the system. There are two valves in series on the household water intake line and they are both open. Between those two valves is a third pressure valve. I don't understand what that is all about. What is the proper way to let water in the system? I've never touched those valves before and they were already open. Should they always be open?

Also, I don't get how the expansion tank above the boiler plays into all of this. There's a drain valve on the tank, plus two valves on the pipe between it and the boiler (again I don't get why all these valves in series on the same pipe). When the system is running the pipe leading to the expansion tank is sometimes hot (all the way up to where it enters the tank), and sometimes cold. But the tank itself never gets hot. Don't know what that means, but maybe it's useful information.

Thanks a bunch for any help.
 
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Old 10-12-07, 08:22 PM
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You want 5 psi at the top, so 34/2.31 = 15, and 15 + 5 = 20. You need 20 psi for your house.

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