i have vaillant boiler mod. ga92140ei when it fires up eithin 1 minit the boilr starts poping loke it was geting to hot. as it continues to burn thr poping gets worse . boiler satisfies on aquatat 180 deg. no air in system, return water is 137 deg. water psi. is 8 psi. what could make the boiler pop while heating?

AUBREY, March 2010