Boiler pressure staying the same ?

Old 03-03-12, 12:27 PM
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Boiler pressure staying the same ?


I have a Hydrother-85 gas boiler. It recently started leaking some water.
So I replaced the expansion tank and the gauge(it got stuck so I had to replace it).

After charging the new expansion tank to 12 psi, I installed it onto a shut-of boiler. Opened the water and the pressure gauge went from 0 to 12 psi. So far so good. Then I started the boiler, and the flames came on, the pressure went up to about 16-17. I left it working for about 5-6 hours now. There is no leakage, but the pressure gauge remains at 16-17 psi, wether the flames are on or not ? -- Is this normal ?

I have another boiler(#2), which also had pressure issues recently, and I replaced the water regulator, and its working fine, but its pressure fluctuates from about 14-19. With the flames it goes up to about 19, then in comes down to about 14 until the flames come on again..

So, should the first boiler also fluctuate or is it fine like that ? Any suggestions ? Like shoul I replace the water pressure regulator ?

Old 03-03-12, 12:57 PM
Join Date: Mar 2006
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Pressure variations in hot water heating systems are a function of the total volume of water in the system, the temperature variations and the size of the expansion tank. A system that has a small differential of temperature fluctuation, small amount of water and a large expansion tank would show a minimal pressure change whereas a system with a wide temperature differential, large amount of water and small expansion tank will show much larger pressure changes. In other words, it is entirely possible that both your systems are operating properly.

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