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Thread: "Superstore" 40 gal hot water tank discharging through overflow - why?

  1. #16
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    If the T&P is the one with the yellow tag hanging off of it on the WH tank, with the perspective available, it is hard to tell if it is installed improperly...it must drain DOWN, not up. Installed upside down could mess things up. You should pick up a water pressure gauge and see what your inlet water pressure is. You can get one for about $10 - select one that has a peak read tattle tale hand, and leave it connected overnight to see what your peak pressure is over a typical day. If it is statically above 80psi, put in a PRV and expansion tank. If it has significant peaks after a lot of hot water use, you DO have a closed system (the water company may have a check valve you don't know of), and need an expansion tank for the potable water.

    Anyway, if that T&P is open, and you don't have excessive pressure or temperature, just replace it! If it's drain is not directly down, fix that in the process.

    The boiler internal pressure looks about what I think is normal.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  2. #17
    DIY Member McG's Avatar
    Join Date
    Sep 2007
    CT, RI


    Here's the replaced T&P valve on the water heater. I believe it is right side down and installed correctly. It has been in for over a week and no discharge.

    Interestingly, I had to get it at a plumbing supply house because the big box stores did not carry the eight inch thermometer T&P only the four inch. It was more expensive, $17 as compared to under $10 for the four inch. I needed the eight inch thermometer because that's what I was replacing. The hot water outlet exits the tank from the same coupling as the T&P valve which adds distance from the valve to the inside of the tank - thus requiring the additional length of thermometer.

    I installed the white expansion tank horizontally from a riser because our water pressure is high at 79 psi and up. The picture is misleading by which I mean, the expansion tank is NOT attached to the hot water riser exiting the tank but from the cold water inlet riser just behind, and at this angle, in line with it.

    All NPT (national pipe thread threads) couplings were taped AND doped.

    Thanks Jim and Red. I couldn't have done it without your support. Nice to have hot water!
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    Last edited by McG; 11-16-2010 at 02:20 PM.

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