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Expansion tank needed?

DIYChrisDIYChris Member Posts: 9
I have a 75 gal State Select DHW heater with HW recirc. Recently, I started getting releases from the T/P relief valve but only at the end of a burner cycle. Thinking the T/P relief valve was failing, I replaced it only to have the same thing happen again. After talking to the State rep, he suggested that I needed to add an expansion tank, i.e., it was not a T-related release but a P-related release. I suspect he is right, but thought I would confirm with others (though I am dumbfounded why this is happening now and I have not seen this before -- nothing has changed in the system that I am aware of).

So, if an expansion tank is needed, I have a few questions/concerns:
1. Based upon a sizing guide I found, something on the order of a 4-5 gallon expansion tank was suggested. Does this sound about right?
2. Most of the expansion tanks appear to be stainless steel in construction: Will this be a material of construction compatibility issue with my copper/brass piping?
3. Any expansion tank brands folks would recommend?
4. Finally, the expansion tank should be oriented vertically with the threaded nipple on top, correct?

Thanks for the assistance!

Comments

  • kcoppkcopp Member Posts: 3,597
    1...sounds fine make sure you pressurize it to the incoming street pressure.
    2.. not a problem.
    3..Amtrol is what I use. Most all are fine.
    4. that is fine.
  • Jamie HallJamie Hall Member Posts: 14,791
    Just to add a bit -- did you, by any chance, recently fix a small drip in a faucet? Or something of the sort? You probably had had something in the system which was acting as a pressure release before!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
    Mark EathertonZman
  • JUGHNEJUGHNE Member Posts: 7,861
    edited May 2015
    A "running" toilet supply valve will also provide the pressure relief and they are sometimes silent.

    Or did the muni water supply pressure increase for some reason?

    Also with the pressure increase at the end of a cycle perhaps you are running up to a higher temp than usual......just enough for additional expansion of hotter water being produced.
  • 4Johnpipe4Johnpipe Member Posts: 479
    How old is the water heater? The anode rod may a dual material type rod and the exposure may cause a reaction to the the treated water from the water company. We have a town by us that requires a specific anode or it will turn the water to seltzer water. An expansion tank will solve the symptom there may be more to the cause though...
    LANGAN'S PLUMBING & HEATING LLC
    Considerate People, Considerate Service, Consider It Done!
    732-751-1560
    email: [email protected]
    www.langansplumbing.com
  • Larry WeingartenLarry Weingarten Member Posts: 2,029
    Hello: Just so you know what you're dealing with, try putting a 0-200 psi gauge on the heater's drain and watch it when the heater is firing. You'll likely see the needle zoom up to 150! If you do add an expansion tank, best to put it on the cold side of the heater where it won't experience heat from the hot water. That should help the rubber diaphragm last longer. You probably already know to pre-charge the tank to line pressure before you install it. They come charged only to 40 psi.

    Yours, Larry
  • RobGRobG Member Posts: 1,850

    Hello: Just so you know what you're dealing with, try putting a 0-200 psi gauge on the heater's drain and watch it when the heater is firing. You'll likely see the needle zoom up to 150! If you do add an expansion tank, best to put it on the cold side of the heater where it won't experience heat from the hot water. That should help the rubber diaphragm last longer. You probably already know to pre-charge the tank to line pressure before you install it. They come charged only to 40 psi.

    Yours, Larry

    Get a pressure gauge with a lazy hand and leave it on for 24 hours and you will be able to see what your peak water pressure is. They are not expensive but they are necessary in some situations.

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