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Thread: Irrigation system causes hot water heater to (almost) constantly run?

  1. #1
    DIY Junior Member medmannj's Avatar
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    Default Irrigation system causes hot water heater to (almost) constantly run?

    Good day and thanks in advance for the wisdom.

    I live in a new home (3 years). During construction, I had them pre plumb for a sprinker system and put in the backflow preventer outside. The "T" for the sprinker system stems from the cold water feed almost at the same location it splits for the cold feed on the hot water heater.

    I have noticed alot that many times (yes, I watch late at night in the basement) that my hot water heater cycles A LOT more on nites when the sprinklers run than on days it does not. I also notice the cold feed going into the hot water heater get really hot too when the sprinklers are running.

    I have had the home builder plumbers check to make sure nothing was cross plumbed, but cold to cold and hot to hot checked out.

    So my quesion, is there any potential that the sprinklers could be pulling so hard on the cold water feed to actually back suck hot water out of the hot water heater (thru its cold feed). And if so, what is best remedy, will relocating the sprinkler feed to cold water FURTHER from the hot water heater help (as the junction for both sprinker and hot water heater cold feed are at the same location)?

    THanks in advance, and i would LOVE to save on my gas bills (in the summer).

    Mike


  2. #2
    Irrigation Contractor Fireguy97's Avatar
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    Mike, In this lifetime I believe that anything is possible, and if it's possible, then it will break at some point. But, without pictures, flow rates, static pressure readings and pressure readings on the pipe when the irrigation system is on and off, your questions being answered could be beyonf the scope of this forum.

    What you are telling us *shouldn't* happen, but i'm sure that it could be possible depending on the pipe, location of fittings, pressure and flow rates.

    You might want to bring in a pro to duplicate it and get pressure and flow readings when the system is on. Get the pro to run the system during the day and test the flow and pressure rates and check the plumbing.

    Mick

  3. #3
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by medmannj View Post
    I had them ... put in the backflow preventer outside.
    That keeps water from an outside source from coming into your house.

    Quote Originally Posted by medmannj View Post
    The "T" for the sprinker system stems from the cold water feed almost at the same location it splits for the cold feed on the hot water heater.
    Have a check valve installed in the line that feeds the heater and your problem will be solved.

    I have the same kind of thing going on here when the washing machine needs water while I am in the shower. For whatever reason, the washer gets priority and I get cold!


    In my own case, I will likely use a swing check to avoid placing any resistance against my circulator pump.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    UNLESS there is someway for cold water, or air, to enter the hot system AFTER the water heater, there is ABSOLUTELY no way to "suck" the hot water out of the tank. To do so it would have to create a vacuum, and that is impossible with a pressurized system. Even IF it could happen the replacement water would have to be cold to turn the heater on. IF you have a problem it is something else, but we cannot diagnose it from here.

  5. #5
    DIY scratch-pad engineer leejosepho's Avatar
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    It is some kind of "path of least resistance" circulation issue, hj, not vacuum. In my own case, the original cold line inside the house is still copper running through the slab, and the hot line is newer pex in the attic ... and the supply line coming in from the street is farther from the washer than from the heater. So, and when the washer calls for cold water while the shower is running, it is easier for the line from the street to get it there by pushing it back through the shower's mixing valve and the water heater.

    The OP's specifics are different, and the plumbers should have installed a different valve in my shower last week, but a check valve will still solve the OP's problem just as well as my own.
    Last edited by leejosepho; 05-31-2010 at 08:09 AM.

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