Pressure Check

RobFurnace

7 year old home, last night I had to change my air bleeder valve as it developed a leak. Changed the valve and opened the water cutoffs. Turned the system on and watched the pressure. It got up to about 26 PSI which is higher than I remember seeing it and this morning (turned off furnace for the night) it had a cold reading of 21PSI. I have a ranch house and everything that I've read says cold PSi should be ~ 12. I have an Amtrol 30 bladder style expansion tank and I'm wondering what my next step should be.

De-pressurize the system and then refill it to see what my reducing valve is set at?

Check the pressure in my expansion tank?

Both??



Any help is appreciated!

Brad White

Dyslexia?

21, 12, whatever....



Seriously though, if you do have a leak-by at your fill valve, yes, isolate it and see what happens.



Agreed, 12 psi should be plenty of pressure for a single-story ranch with room to spare. Do you have a tankless coil? That is a possible source for higher pressure water intrusion if a pinhole leak.



 Is there any collection under the relief valve outlet? (What Mark E. calls a "witness cup".)



I would wait until it is warmer out and the system is cold. Bleed down the system to 12 psi but then put a Schraeder gauge on the air side of your expansion tank. That should also read 12 psi. (Automotive check gauges are handy for this and with good range, especially the digital ones.)  So yes, just as you said. Then check your automatic fill valve setting. That is a good suspicion. If you have an isolation valve on the tank, check that it is open. (I leave them open and remove the handles. Kids these days...)



For a small system, assumed copper pipe not over an inch diameter, I would be surprised if an Amtrol 30 would not serve that system volume well with a margin. 



It could also be that the tank diaphragm is broken, leaving you with no cushion for expansion. If you WERE home when this happened, it sounds like the onset of peristolsis prior to a race to the porcelain throne. You would have noticed it. But if you have automatic air removal, this charge of air (a roving expansion tank at large out in the system), would have been expelled at least in part.



So, I suspect your fill valve or other inadvertent leak path forcing water into your system. If that is the case and it is unregulated city water pressure at the source, your system would fill to relief pressure, the valve would dump and the situation would repeat.