Posted by Harold Kestenholz - Hydronic Network on November 17, 2001 at 08:37:52:
In Reply to: Re: How to refill the system - keep main water on ? posted by Allan Weinman on November 16, 2001 at 22:00:57:
The boiler water pressure changes with the season because water expands when heated and shrinks when cooling, so the expansion tank size determines the pressure according to the temperature. Most boilers are filled using a pressure reducing valve set at 12 psig, so the cold pressure is usually 12 psig. As long as the pressure does not rise any higher than 24 psig when the boiler has a 30 psig relief valve, the system is pressurized properly.