On Nov 28, 7:52*pm, "jimmy" wrote:
For the past 40 years I have installed 4- 40 gallon hot water tanks (natural
gas) in my home.
Today I picked up a new 30 gallon tank, installed it, fired up and could not
believe the pressure rise as temp increased, went to 140# and still going at
120 deg temp
My incoming pressure is usually 90psi, give or take 10 #
I know I am going to need a press reducing valve, either for the entire
system, or the hot water tank itself, or an expansion tank for the hot water
tank.
Question is why in the world am I having pressure rises like this on the new
tank, and never had this problem before ?
thanks


Your water heater cannot create a system pressure rise unless your
water system is a "closed" system.

Do you have a check valve or back-flow preventer somewhere in the
system?
If so you need a system pressure relief valve or an expansion tank.

Run some water out of a hot water valve in the bathroom or kitchen
(about gallon or so) and see if the pressure drops.

My best guess is that the expansion of the water in the water heater
from cold to hot is pressurizing a closed system.


cheers
Bob