My system is going up to 28#'s of pressure when I heat up the storage and the circ's are on. I have 2 expansion tanks. One is an Extrol SX-90 which suposidly has 44 gal of volume. The other is a #90 which has about 14 gal of volume. Together I should have 58gal for expansion. I have radient floor heat, 2 radiators, 500 gal of storage and an econoburn 150. I'm gonna guess I have about 600 gallons in the system. Any ideas why the expansion tanks are not doing their job? They are factory set at 12psi and the system is set at 12psi when cold and circ's are off. Is the pipe size going to the expansion tank critical? Does air below the bladder need to be purged? I just piped the tanks into the system and fired it up.