My the check valve started to show signs of water the first day I used
my new heater. So I turned down the thermostat. It still run water.
So I turned it way down, and it still does it. When they installed the
new heater, the plumber checked the inline pressure and said it was
fine. So do I have a bad check valve on this heater? Is a thermal
expansion tank necessary? How hard are they to install?

JaKe