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OT: Water Heater Without Water

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  • OT: Water Heater Without Water

    I had to flee Harvey and my town is now without water. I did not turn the gas off on the water heater when we left. Does anyone know how long it would take for a water heater tank (40 gal?) to go dry with no water coming in? I am mildly worried.
    Paul A.
    SE Texas

    Make it fit.
    You can't win and there IS a penalty for trying!

  • #2
    You should have nothing to worry about. As the water temp rises it will expand into your inline expansion tank and that is it. Also there is a back flow valve so even if you get zero water pressure at the water main you'll still have pressure in your system.

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    • #3
      I was not worrying about where it would go when it expands. I was worried about running about water, going dry and perhaps overheating if the over temperature controls fail. Melt down, house fire, that type of stuff.

      I know the loss should be small, but even a small loss can add up to something over time. Just wondering how much time would/might be involved.
      Paul A.
      SE Texas

      Make it fit.
      You can't win and there IS a penalty for trying!

      Comment


      • #4
        Paul I bet you will be alright for quite awhile if it's in a low spot of the house and everything drains down to it,
        just what's in the heater and the upper pipes alone would probably allow for ample reserve to keep the thing from going supernova,,,

        I just had a similar worry with mine, went on a week long trip and I usually always cut the water supply to the house just in case one of my old pipes shoots craps, I also forgot to turn the heater to just pilot light mode, kinda worried about it some even though my heater is the lowest thing in the plumbing I was concerned because it was so old and I gridlocked my system, I have everything shut off and then stopped the back feed to the water supply line so hydrostatically locked the plumbing with no room for expansion, do to the tank being so old I then imagined the lower part blowing out and springing a leak after a heat cycle expansion mode, then all water would be lost in a hurry and yet the tank would still be trying to heat the water, with no water the tank would overheat yet maybe not even sense it to be able to shut off...

        anyways - got home and all was well but yeah was a stupid thing I did and unlike you I was not having to leave in a fury...

        good luck to you hope things work out.
        Last edited by A.K. Boomer; 09-01-2017, 02:04 PM.

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        • #5
          If you have a 40 gal tank, then maybe 1/4 to 1/2 gallon (guessing at most) might expand outside. You will never loose enough water to disrupt the thermal control loop.

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          • #6
            Originally posted by Paul Alciatore View Post
            I was not worrying about where it would go when it expands. I was worried about running about water, going dry and perhaps overheating if the over temperature controls fail. Melt down, house fire, that type of stuff.

            I know the loss should be small, but even a small loss can add up to something over time. Just wondering how much time would/might be involved.
            It should be fine for several years.

            Comment


            • #7
              Again totally depends on it's position in regards to the rest of the plumbing system...

              Im not positive but does not one of the lines going in or out of the tank have an internal pipe that runs close to the bottom of the tank? if the tank was higher than the main water inlet that's all it might take to percolate a little water out each heating cycle...


              edit;

              yes the cold water inlet is the one and that's incidentally the one that could toss it back into the dry inlet system "if" maybe the anti-back flush valve was frozen and inop. or just never installed.

              they call it the cold water "dip tube" https://www.thespruce.com/anatomy-of...heater-1824894

              also keep in mind an un- pressurized tank will boil allot quicker and cause that unwanted percolation,,, then you got one big fancy coffee pot that gets dryer and dryer inside every cycle...
              Last edited by A.K. Boomer; 09-01-2017, 02:32 PM.

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              • #8
                You have nothing to worry about from your water heater friend - hope you are able to resume life as you knew it soon.

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                • #9
                  The gas valve has a built in high water temperature "Fuse". I have a 12 year tank 40 Gal Whirlpool that if I don't drain every year. The buildup from the anodes corroding falls on the bottom of the tank. It will bridge the gap between the temp probe and bottom of the tank and overheat the gas valve and it closes the gas valve. It is permanently closed. The only way to fix it is to put in a new gas valve.

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                  • #10
                    H380 does my tank have that? My tanks a 1983!!! have no idea how it's still making it but works like a charm...

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                    • #11
                      Yep it should. The gas valve screws in to the tank. It has a SS probe that looks like a commercial thermometer. I am on my 3rd as you can see.

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                      • #12
                        Unless your heating your water with an open bucket over a fire, the system is closed and can't vent/expand anywhere except into an expansion tank on the hot-water side. Even when it "expands" the hot water tank is still full of water -- the volume just increased a little bit due to the temperature then returns back into the tank as it cools down.

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                        • #13
                          Don't know about Paul but me no gots an expansion tank...

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                          • #14
                            Do you have a well pump and a pressurized holding tank? If you're on city water, you should also have a check-valve preventing back-flow into the city supply. Without an expansion tank, you're just putting stress on your plumbing system every time the water in your heater thermally expands then contracts as it cools off. If you have air in your system then this acts like an expansion tank.

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                            • #15
                              This is a very old system - iv looked for long standing vert. pipe thats a dead end and would be used to hold air but have never seen any of it,

                              im on city water...

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