Old 12-30-06, 04:13 AM
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Location: USA
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I have a gas fires hot water boiler. When it comes on I hear a rush of
water! I have cast iron baseboard heat. Is this something I need to bleed
the radiators for? If so do I bleed the radiators with the heater on or off? I
don't hear a lot of banging in the pipes and all the baseboards are hot. I
would appreciate all advise. Thank you in advance .
Old 12-30-06, 06:19 AM
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Sounds like you might have air in the system. You should first check the pressure on the boiler. If the gauge works, it should read 12-20 psi. There is a pressure reducing water feeder that allows water to feed into the boiler when the pressure drops below 12 PSI. If the pressure is low, make sure that the valve before and after it are open. If they are, you might have a problem with the water feeder. If your pressure is fine, then you might have another problem. You should have an air vent or two. There should be one on the air scoop (assuming you have one). Make sure it is open. There is a threaded cap on the top of it that should be a couple turns above closed. If it leaks more than a couple drops when opened, it needs to be replaced. Also, where did the air come from if the pressure was above atmospheric? One possibility is that the expantion tank (usually located below the air scoop) could have a ruptured diaphram. To check this, tap on the side of it. If it makes a tinny sound, like tapping on an empty tin can, it is most likely fine. If it makes a deeper sound, like tapping on a soup can that is full, it is probbably in need of replacement. If your relief valve has blown or has been dripping recently, and if the pressure on the boiler goes above 20 PSI, that is further indication that it may have failed. The relief valve will often blow off if the tankless coil (assuming you have one) is perforated, or the water feeder is leaking by. If the pressure is above 12 PSI, you should be able to bleed the air out from the radiators. If the pressure is too low, you will more than likely let more air in. How many stories do you have? If you have 3 or more, the pressure may need to be increased. Every 10 feet above the water feeder, the pressure drops by about 4.5 PSI, so if you have 12 PSI at the boiler, and 3 stories, the baseboard is acctually in a vacuum. As with any question, the more info, the better.

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