Rheem Water Heater has me stumped!

Discussion in 'Water Heater Forum, Tanks' started by lizzydog, May 5, 2009.

  1. lizzydog

    lizzydog New Member

    Messages:
    4
    Heater 3yrs old
    electric
    30 amp double pole breaker
    120 volts each leg breaker
    120 volts each wire at heater
    new thermostat
    new elements
    120 volts each side thermostat
    120 volts each side of top and bottom element
    reset pushed
    NO Hot Water
    Help

    Thanks
    lizzydog
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Measuring each leg of a 240 volt circuit, to ground or neutral, will throw you off. You never know when you are reading across an open.

    You need to see 240 across the two terminals of an element. If it is not 240, it will not heat....period. Something is open.
  3. Cookie

    Cookie .

    Messages:
    5,660
    Location:
    .
    Try turning the breaker all the way off and then, all the way back on. Check the top 2 scews of the top thermostat at the same time and you should have 240 volts.
  4. Thatguy

    Thatguy Homeowner

    Messages:
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    Location:
    MD
    Each 4500w element should read 240²/4500 = 13Ω.
    Voltages measured with respect to ground?
  5. Cookie

    Cookie .

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    12.80 you rounding?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Well, few meters out in the field can read that accurately, plus, the resistance will be different than that when cold verses energized...but, close enough.

    Don't try measuring resistance with the power on unless you like sparks and value the meter (the fuse should blow, but you never know).
  7. Thatguy

    Thatguy Homeowner

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    MD
    That I be.

    There is also Significant Figures, which is a little harder to 'splain.

    120 could mean between 119.5 and 120.4 [3 significant figures] or it could mean 115 to 124 [two significant figures] in which case the '0' is just a placeholder. I took it to mean two figures and so the answer should be the same number of figures. Since the 120 varies by ±5% or ±10% this is plenty close.

    We nerds get around this by using scientific notation, so 1.20 x 10² is 3 figures and
    1.2 x 10² is 2 figures and 1.20000 x 10² is 6 figs.
    Last edited: May 5, 2009
  8. Cass

    Cass Plumber

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    5,980
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    Ohio
    WoW...were trying to fix a water heater not fly to the moon....
  9. Thatguy

    Thatguy Homeowner

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    Rum does that to me:D
  10. lizzydog

    lizzydog New Member

    Messages:
    4
    Rheem waterheater has me stumped

    Thanks for all the information. The new 30 amp double breaker was bad.

    lizzydog
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,270
    Location:
    Cave Creek, Arizona
    heater

    WHO measures resistance? If the element has 240 volts and the amperage is ZERO the element is bad. It it reads in the neighborhood of 18 amps it is good. AND both leads have to read the same amperage.
  12. Thatguy

    Thatguy Homeowner

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    Location:
    MD
    Nah, he's on first :D

    I figured more people have ohmmeters than clamp-on ammeters and more people prefer to make unpowered measurements.

    240v/18A = ~13Ω.
    Last edited: May 9, 2009
  13. Redwood

    Redwood Master Plumber

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    7,453
    Location:
    Connecticut
    I test like HJ does...
    Seems to work for some reason...
  14. Thatguy

    Thatguy Homeowner

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    What's also is in your favor is that a water heater element doesn't fail in many different ways.

    I doubt that the element resistance changes in value and it's unlikely that the resistance element shorts to the grounded element tube because of all that ceramic insulator packed in there, so your choices for resistance/current flow are 13 Ω/18A or infinity/zero.

    It's pass/fail.:cool:
  15. Redwood

    Redwood Master Plumber

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    Oh elements do short to ground.
  16. Thatguy

    Thatguy Homeowner

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    In that case troubleshooting by CB is easy!

    The ratio of failing by opening to failing by shorting is, would you say, 90/10? 60/40?
    I don't fix enough of these to offer odds.
  17. Redwood

    Redwood Master Plumber

    Messages:
    7,453
    Location:
    Connecticut
    Not always.
    Lets say the short occurs at the center of the element.
    The element will coninue to work normally without popping the breaker however, since only one side of the power is switched by the t-stat the element will continue to heat on 120 volts after the t-stat shuts off.

    The hot water if not used will end up being quite hot...

    This is the reason for checking both wires to the element for amperage to make sure they match.
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