behind every boiler there is a orange or red colour vessel called as expansion vessel.
either there is no air in it or the diapharam is split
when water gets hot it expands. There no room for expansion so the pressure increases and water goes to the pressure relief pipe to outside
there is a valve on the vessel just like car tyre valve
air pressure should be about 10 -15psi
to fill the air in the vessel you will have to make sure the presure is zero on the pressure gauge of the boiler
then pump up air up tp 15psi.after that fill the water in the boiler and fire it see what happens
heatingdoc, February 2009
