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Thread: Hot water running out too quickly

  1. #1
    DIY Junior Member jhqpzjg's Avatar
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    Default Hot water running out too quickly

    I have a Rheem mod# 21V40-7 gas fired 40 gallon water heater. The hot water seems to run out too quickly for the size of the heater, which is particularly noticeable in the showers. I find myself constantly adjusting the temp in the shower toward hot while I'm in there in order to keep it from going luke warm. I noticed this problem first myself, and now have the same complaint from tenants now living there, without prompting them.

    I first checked for anti-scald devices in the shower valves, which I removed for troubleshooting. I also raised the temp on the hot water heater itself to just below the max. Neither step seemed to help the problem significantly.

    Any suggestions on cause or further troubleshooting would be greatly appreciated.

    Thanks,

    Jason

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    A 40-gallon tank can supply maybe 30-gallons before it starts to cool off (when working properly). That's maybe 12-minutes or a little more if your showerhead is the 2.5-gallon max type (depending on how much cold you need to add).

    If the thing was installed wrong, you could start to cool things off very quickly (i.e., the cold going into the hot port rather than the cold). Or, if the dip tube is either defective or missing, the thing will not be directing the cold water to the bottom of the tank, and it will mix with the hot and cool things off quickly.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    You didn't say how old the tank is. If it is a few years old, there is a good chance that the dip tube has failed inside the tank. It is under the inlet pipe on the tank and forces the cold incoming water to the bottom. If the tank is in otherwise good shape, the dip tube can be replaced.

  4. #4
    In the Trades Gary Swart's Avatar
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    I'm late getting into this, but I will reenforce the previous suggestions on the dip tube although you could be just trying to use too much hot water too fast. The dip tube is easy to check, it hangs under the cold water inlet. If it is broken off, it's quick, easy, and cheap to fix. If that's not it, you aren't out too much time and no expense in checking it, so that's what I'd do first.

  5. #5
    TROJAN WORLDWIDE SALES RP MACPLUMB 777's Avatar
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    Or you could just fix the problem by changing the moen cartridges in any single handle faucets you have in the house
    when the cartridges get old and worn they allow cold water bleed over though the valve causing your problem

    MACPLUMB 777

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    35 YEAR MASTER PLUMBER, HEATING, ELECTRIC, DRAINS, FIRE SPRINKLERS, WATER HEATER
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  6. #6
    In the Trades Gary Swart's Avatar
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    I'd still check the dip tube before rushing out and buying cartridges or doing expending any money. Sure, it could be something else, but check the easy things first.

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