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Posted by HeatPro on May 22, 2006 at 10:42:38:
In Reply to: Re: copper tube boiler groaning/vibrating posted by Dave on May 22, 2006 at 09:54:22:
I surmise that the needle vibrating on the circulator inlet is an indication of cavitation (changing state from water to steam and back again), which was what probably killed your 0012. It is a flow rate problem in that circuit, again, more likely related to not having a balance valve to set the resistance on the outlet side of the circulator
AND the heat path in the boiler on one or more tubes. Opening the bypass to the tank would INCREASE the problem by adding hot water back to the boiler instead of cooler tank temperature. You might stop this problem by using a tank thermostat to keep the boiler off while the water in the tank is 140F or so.
35 feet height from the boiler gauge means that the boiler fill pressure should be 20 psig with an expansion tank pressure of 18 psig, so that might be set right for now. Another or larger expansion tank could let you set the minimum to 25 psig to bring the boiling/cavitation temperature higher. Sizzling boilers are often solved by raising the boiling point by raising the pressure.