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Posted by HeatPro on May 21, 2006 at 16:19:17:
In Reply to: Re: copper tube boiler groaning/vibrating posted by Dave on May 21, 2006 at 11:40:37:
The expansion tank should have the pressure at 2 lbs BELOW the cold fill pressure, so it has some water volume accepted to make up for air venting. Find the pressure at which there is no noise in the boiler. You probably have it set at that point now.(This is why when the water cooled when heat was not needed upstairs the pressure droped to 10.)
Drop the pressure in the boiler to 5 lbs lower than that non-noise pressure. As you have anti-freeze in the system capture the water you take out so you can pump it back in. Play with the expansion tank pressure until it is two lbs below the pressure you got no sizzling. Then refill the system to the pressure where there is no noise.
Ten pounds pressure means that 10 - 4 = six pounds of water to fill the sstem to the top plus 4 lbs to be able to vent air out the highest point. Six pounds of fill pressure means that the highest point in the system should be no higher than 12 feet higher than the gauge. It is probably too low at 10 psig.
http://64.226.150.132/hydronic/service/purgeair.htm#fill