Originally Posted by Protagonist
The newer Atwood water heaters have a mixing valve in the system to add cold water at a ratio of 2 hot to 1 cold, even before you get to the mixing valve at the faucet. The heater produces water hot enough to scald otherwise. It's a gimmick to say thay can get nine gallons of hot water out of a six-gallon heater. Since there is that extra mixing valve, if the water heater overheats, you can over-pressure the cold side as well.
I now understand; I just finished all new plumbing in my Argosy, so, as a test for pressure and leaks, I hooked the water line at my house with a 40# regulater, and placed a pressure meter on the kitchen sink faucet. The pressure was a steady 40#, but after the water heater cycled, the pressure was 60#. Now if I would not have had the 40# regulater in the waterline, the pressure would have been 60# before hot water. Hot water would have taken it up to 80#. Is this still safe? Or does the overpressure valve kick in before 80#?