AO smith doesn’t require an expansion tank.So... finally my daughter calls the company that installed the water heater. The guy comes and admits that they likely didn't pump the tank bladder up to line pressure initially and that since there is no pressure reducing valve in place, the tank might not be needed in the first place. Claims that AO Smith requires the tank for warranty purposes. Installs new tank with bladder pumped up to 80#, 10# over tested line pressure, leaves a fat bill which my daughter pays. Now she agrees that if this tank fails I can put a plug in place of the tank.
Probably ignorance more than a lie from the installer. It sounded good to him