Does my water heater have a bad thermostat?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by cdwz, Aug 18, 2008.

  1. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    We have a fairly new water heater (around 6 years old) that keeps shutting itself off. Around once a day I have to press the reset button on the high limit switch, and we have all noticed a significant increase in water temperature coming out of the taps.

    I've used a multimeter to test the thermostats and the elements, and both seem to pass the test, but maybe that doesn't mean anything. If I change the temp setting on the upper thermostat at all, the limit switch trips the second I move the dial.

    I'm pretty sure this is a bad thermostat, but I want to make sure there isn't something else that might be bad that I'm overlooking.

    Any advice is appreciated.
  2. Redwood

    Redwood Master Plumber

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  3. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    YES. or a bad Element. Or both.
  4. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    Well I tested the elements using a multimeter, and they have no resistance when tested through them (one tester lead on each screw of the element) and infinite resistance when tested to the mounting bolt. I know the latter of those two is correct, but it seems like they should have at least some resistance. :confused:
  5. Redwood

    Redwood Master Plumber

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    Your meter may not be accurate enough to dicern the resistance.
    Depending on the wattage of the element it may be around 12 -13 ohms.
  6. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    Ahh, good point. It's a cheap, 15-buck analog meter.

    I'll replace the upper thermostat since that's the most likely culprit. When I press the reset button on the upper t-stat, it's always blazing hot, and this element is not even supposed to kick in very often.

    Thanks for the help.
  7. Redwood

    Redwood Master Plumber

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    Location:
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    Did you check the link to the other thread I provided above.
    As I stated this is a safety related problem and at this moment you are relying on the reset and the T&P to prevent the same thing from happening at your house.

    I would highly recommend calling a plumber to diagnose and correct this problem.
  8. MACPLUMB 777

    MACPLUMB 777 TROJAN WORLDWIDE SALES RP

    Messages:
    679
    Location:
    Houston, Texas, United States
    Water Heater Explosion ! ! Update ! !

    No Just A Bad Plumber Who Doe's Not Know What To Check For ! !


    That Said One Of Your Elements Has A Small Bad Spot, Like A Piece Of Fruit,

    One Side Always Has 110 V. To It
    The Other Side Is The Switch Leg, With A Bad Spot On Element It Goes To Ground Against The Inside Of The Tank Which Means It Is Constant Low Heating
    During Periods Of Not Using Hot Water It Trips The Overheat Limit
    Switch Thats Why You Get Extra Hot Water Out The Faucets
  9. MACPLUMB 777

    MACPLUMB 777 TROJAN WORLDWIDE SALES RP

    Messages:
    679
    Location:
    Houston, Texas, United States
    Water Heater Explosion ! ! Update ! !

    You Should Look At The Post 5-4-3-2-1- Lift Off Before Risking You, Your Family, And Home On D I Y Type Repairs As Opposed To Calling A Lic. Plumbing Contractor To Do The Work ! ! !


    If As You Posted You Have Open Legs Across Both Sides Of Element Then It's Is Burnt Out, In Which Case You Would Not Have Any Hot Water ! ! !
  10. Redwood

    Redwood Master Plumber

    Messages:
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    Location:
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    Um Jerry that is the thread I linked.

    Man that house looked like it sneezed!
  11. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    I don't think I have to worry about an electric water heater exploding. A gas one maybe. Thanks for the link though.

    The breaker's off for what it's worth. We can live without hot water until I get the problem fixed. The showers are luke warm without it because it's 140 degrees plus in the crawlspace where the pipes go. Just gotta shut off the tap during suds up as not to run out of the crawlspace-heated stuff.

    Last edited by a moderator: Aug 19, 2008
  12. Redwood

    Redwood Master Plumber

    Messages:
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    Location:
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    It doesn't matter how it heats up...
    The end result is the same...
    All that is betweem you and boom, is that red reset button and a t&P valve.
    The effects of thermal expansion and steam pressure do not dicern the method of heating.
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    heater

    I do not measure resistance of the element. I test if it should, or should not, be heating and then if it is. The reset button is independent of the thermostat setting, so if your description is correct it could be a bad thermostat.
  14. kingsotall

    kingsotall Plunger/TurdPuncher

    :eek:

    Sounds like no matter what he doesn't need a plumber. Remember, these folks try to lead you in the right direction. If it's DIY do-able then they say so. If they recommend a pro, I'd listen to 'em.
  15. GrumpyPlumber

    GrumpyPlumber Licensed Grump

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    No insult intended to the homeowner here, but in lieu of the incident in Phoenix I wouldn't advise anyone to so much as adjust the temperature on an electric water heater.
    On a 6 yr old water heater, if that T&P isn't functioning properly and the breaker is already tripping on the heater, I'd strongly suggest he get a pro.
  16. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    I understand that everyone's trying to help, but I don't see how an electric water heater with no power (i.e. the breaker is still off) that's sitting in a basement at 70 degrees is going to explode. If so, I'd definitely like to know about it.

    The local plumber wants $325 to replace the thermostat, which he diagnosed as being bad by listening to my description of the problem on the phone (he also said that elements "almost never go bad", so I shouldn't worry about them at all). :rolleyes:

    So you can see why I'm considering replacing it myself. I'll probably replace both, just to be on the safe side, since I can't determine which one is bad by using any of the testing methods I've found.
  17. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    Looks like this is a non-issue, as my water heater is now being fixed.

    I'm having some tile work done in one of the bathrooms, and the tile guys managed to run a screw into one of the pipes in the master bathroom. They ran downstairs to shut off the water, and then called in a plumber whom they usually use.

    The plumber fixed the damaged pipe, then went downstairs to turn the water back on and saw my water heater half taken apart. They called me to ask what was up with it, and I explained the problem. The plumber said, "Heck, I've got a thermostat that'll fit that on my truck. Want me to go ahead and fix it?"

    I said yes, so now for $100 it's being fixed (and tested) as we speak.

    Thanks for the advice everyone. Hopefully I won't go home to any water damage tonight! :eek:
  18. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Well then perhaps this video of Mythbusters launching an electric water heater might convince you otherwise...
    http://www.youtube.com/watch?v=JmJoyuUJj2Q
  19. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    watts.com video called "Danger Lurks" free down load. Makes Mythbusters stuff look lika a cap gun.

    Very few things in your house have the potential to destroy your home and kill everyone in the house. Your water heater is one of those things.

    Watch the video and let us know how you feel after.
  20. cdwz

    cdwz New Member

    Messages:
    33
    Location:
    Arlington, Virginia
    Cool! But how does the pressure increase when there is no power to the elements? Is there something connected to my water heater that I'm unaware of? I thought for sure that with the breaker off, and no electricity to the heater, I was safe!
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