Posted by Harold Kestenholz - Hydronic Network on July 27, 2001 at 12:35:50:
In Reply to: Re: Boiler water pressure - one more question please posted by nickj on July 27, 2001 at 10:52:15:
At 5 psig there is a high chance that air will enter the system unless all the baseboard is below the boiler. There may be a problem with the gauge; it may need replacement. Verify that the gauge is good by comparing it with a good one.
You can drain the system to bring the pressure close to zero on the gauge and pump the expansion tank with air to 12 psig with a bicycle pump. The Amtrol combination will then permit water to enter until the the fresh water line pushes the valve closed against the bladder pressure inside the tank, preventing the valve from being open. Then you would purge air, then set the heat up a while to circulate bubbles to the air vents and get rid of corrosive oxygen from the water. Then observe that all is well.
You can then go through the observation to see if the relief valve will lift as in the post above. If the relief valve opens while the expansion tank bladder is good and properly pressurized, the expansion tank is too small.