Leak at W/H TPvalve-Add a Pressure regulator before an Expansion tank?

The Tank Leak at W/H TPvalve-Add a Pressure regulator before an Expansion tank?

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    Hi folks,

    I need your help in finding the root cause for the leak on a Pressure Relief valve rated at 150psi.

    I have 2 50 Gal Water heaters installed in Parallel in my garage(as I can turn off cold inlet on one heater, and still get hot water-turning off both inlets shuts down Hot water flow).

    On one of the 2 year old tanks the Pressure Relief Valve (PRV) is leaking now, which was replaced a year ago due to similar issue. Shutting the cold inlet and throwing PRV to release several times doesn’t help.

    My own gauge says Water pressure is between 90-110psi range when heater is idle/fireing. Seems high to me. A year ago the city cked it and said pressure was normal, but I cannot remember the PSI then.

    I’m pretty sure I have a backflow preventer at the street meter as the neighborhood is only 10 yrs old, and confirm I have no expansion tank, nor a Water Pressure regulator (unless city installed it at the street)

    Since this is the 2nd PRV on with the leakage on the same 2 yr old heater, I’m thinking the root cause is excessive water pressure.

    So, my questions are…In order to verify the root cause, (since the PRV is just a symptom),
    1. should I have a plumber ensure there is a water pressure regulator is installed first at the street, and verify “normal” pressure at about 70psi, before I walk down the Thermal expansion tank route inside the house?

    2. OR Should I install a expans tank, and a new PRV….? or do #1 and #2-seems extreme.

    2a. If you think I should install a expansion tank, should I install 2 of em, one per water heater inlet or just a single exp tank on one of the heaters inlet?

    Thanks in advance,

    Randy Schuyler

    Anything over 80 psi is bad, and even though the PRV is rated to 150, it might trip lower than that.

    You don’t need a plumber to do a little detective work. With a water pressure gauge — ten bucks, you can probably find out all you need to know. There is a Tanklet on this, but I’m going to repeat some of it here just for fun.
    And at that, you should still go there for the details of the tests you should make. It’s the one titled Temperature/Pressure Relief Valves.

    The first is static pressure. Again anything over 80 is bad news for everything in your system: water heater, plumbing, appliances.

    The next is thermal expansion. You can read about that in Tanklets. If you do need an expansion tank, make sure it is charged to line pressure or it won’t work. Happy Tankleting…..

    Randy Schuyler


    my bad!!!! I do NOT have a backflow preventer, nor a Pressure Reducing valve.

    reading the tanklets, I think that a Pressure Reducing VALVE would be the first step in bringing down the 100psi pressure all thru the house.

    If that doesn’t help, then I will go the expansion tank route.

    NEXT question: Are there differences in quality between Pressure Reducing Valve manufacturers?

    THE PRV will go in a water main can down 2.5 feet in my front yard where the water line resides. I’ve heard that some cast PRV will corrode and fail in the ground so am looking at a plastic cartridge type from honeywell.

    Here is the website for the PRV:

    Are they any differences of quality between the cast WATT type and this Honeywell type? Opinions?

    There is arepair kit number is K05A1017 and they are about $28 each


    Randy Schuyler

    The backflow preventer is usually something city water companies require to keep something happening in your house from contaminating their main. I wouldn’t worry about that part.

    The PRV is more important, since you want to get the pressure down below 80 psi. You may then also need an expansion tank charged to the line pressure (they come precharged only to 40 psi).

    Sadly, I’m totally unqualified to judge between different makes of PRVs. Maybe Larry can help. He knows more things about more things than anybody I know — and he gets tired of hearing me say that!:shock:

    Randy Schuyler

    Larry Weingarten

    Hello: Maybe I know enough to be dangerous 😛 I wouldn’t install any reducer in a can/box below grade. It’s asking for trouble. Put it where it’s unlikely to freeze or be underwater and make sure you leave enough room around it so it can be serviced. Does your water line go into a basement? Putting the reduced in a friendly place allows you to use whichever reducer appeals to you more.

    So, I’d install a reducer, set in the 50-60 psi range and then install an expansion tank in a cold line. It needs to be sized for the total volume of all the hot water in your system.

    Yours, Larry


    OK, folks, I installed the Pressure Reducing Valve(see link above) between the house and the main on the curb. PSI going into house is at 60 psi. (thinking progress was made…) 🙂

    New Problem-Now my in house Water pressure goes from idle 60psi to 150psi during both 50 gal WHs firing!!!:shock:

    Thats a 90psi increase in pressure measured at outside hose bib and at WH drain bib!! Pressure can be released if I turn on the cold tap faucet at about 10psi per second.

    Impact: T and P valve starts draining at about 110psi on one of the two WHs.(not both)

    Question-IT appears this new PRV doesn’t have a bypass, so will a Expansion tank be able to absorb the 90psi increase, or should I proceed to a Govenor 80 instead???? Any advice on Expansion tank sizing?:?

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