I got the scoop today about what happened at the church explosion.
Forgive me for technical errors but it went like this:
The high limit on the aquastat stopped functioning at a point sometime in the past and the company that serviced the boiler a few days earlier didn't check for it during the servicing procedure and didn't catch it. Also the pressure relief valve was stuck closed and wasn't caught either.
A water leak and loss of water in a zone piping caused the boiler to continue to run because the tstat wasn't satisfied and since the high limit switch stopped working, the boiler continued to run up to about 260 degrees. As the pressure increased, the relief valve didn't release pressure until it finally gave way at 45#. At that point the superheated water blew out and "flashed" into steam, which the inspectors determined to be about 750,000# per psi, which blew a nearby 4 inch block wall 2" off plumb. The block wall was put in by "somebody" when they removed a supporting pillar for the 2nd floor of the church. Being 2" off plumb, the wall collapsed and the entire church collapsed internally, up to and including the roof. The gauge was found in the debris and the pressure needle was frozen at 45#.
So, the moral of the story is: Check your high limit switch and pressure relief valve when you service your boiler.