Weil McClain Boiler pressure too high

Have a 20yr old Weil McClain boiler for hot water baseboard heating. The overflow valve is open with hot water running. The pressure gauge reads 33 lbs. The pipe connecting to the Amtro hot water storage tank (40 gallon) seems to be running nonstop because one can hear the sound of running water.
Two weeks ago, replaced the overflow release valve and 5 gal expansion tank and the system worked until today.
Hope somebody can help.