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Two Electric Water Heaters Tripping at Same Time

Steamback
Steamback Member Posts: 32
I have a situation which I find somewhat baffling. At this site there are two electric water heaters plumbed in parallel. They were operating fine for a few years but recently, about once/month, both tanks are tripping (reset button on thermostat) at the same time. All I can think to do is replace both thermostats and both electric elements. I'm wondering though, could the problem instead be something related to power quality from the Utility Company? The site does also have a solar electric system installed...could the solar inverter be a cause? Has anyone encountered before a situation like this where more than one water heater trips at the same time, repeatedly? Both water heaters are on independent circuits and not connected electrically, except through the service panel, of course. Any thoughts are appreciated.

Comments

  • Larry Weingarten
    Larry Weingarten Member Posts: 2,148
    edited January 15
    Hi, Do you have any way of knowing hot hot the tanks are getting? Something as simple as a split sheath on an element prevents it from fully shutting off, so it could be non-stop heating until the limit trips. I think I'd take a volt-ohm meter and test all elements for leaks to ground... but only if you're good around 240 volts and have power off and one wire disconnected from the element being tested. Hard water, recirc line, poorly connected thermostats... various things could be helping cause this...also, coincidence happens! >:)

    Also, you posted this in solar. Is solar preheating the tanks? Could the preheat be hot enough to trip the limits?

    Yours, Larry
  • hot_rod
    hot_rod Member Posts: 14,786
    The temperature snap discs? Does both the temperature control disc and the high temperature limit open?
    Seems, like Larry indicated, it has to be a temperature related issue, what is the temperature of the tank or water when they trip?
    Those snap disc controls have been around for a long time, they are fairly reliable.

    Put a clamp on amp meter on the element wire, maybe it is pulling a very high current and over-heating the control, although the breaker should trip under that condition. What size breakers feeding those dual tanks?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 15,849
    If they are actually tripping at exactly the same time... it almost has to be electrical, not temperature. I mean, I believe in coincidences, but that's just too much. Further, it almost has to be something common to both tanks, or a problem in one which feeds back through the common switchgear.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,141
    edited January 15
    Happens about once a month? I think it’s a Lunar thing
    Nothing to do with Solar
    Or what Larry or Bob or Jamie said.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    HomerJSmith
  • mattmia2
    mattmia2 Member Posts: 2,996
    I would have thought the t-stat was 2 pole but from Larry's comment i gather they are not. If one tank is overheating relatively quickly it may trigger the limit but only once it is significantly overheated since it takes some time for the heat to migrate to the t-stat then either thermosiphoning or a recirculation system moves the overheated water in to both tanks.
  • JUGHNE
    JUGHNE Member Posts: 8,315
    One overload could trip without anyone knowing it. As the other WH was then over worked to keep, it may have over heated and tripped later. With them both tripped one assumes it was a spontaneous event.

    Being in parallel does not guarantee they have equal flow, one could be doing most of the work until it overheated. Then the remaining tank overworks. Is it plumbed perfectly for parallel? Pipe lengths and fittings differences will induce more flow in one than the other.

    Also without some use/flow the water will stack up from the lower element and upper tank water will overheat.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,008
    Could it be as simple as the thermostats are set too high?
  • PC7060
    PC7060 Member Posts: 317
    Voltage drop in service line could cause units to pull high current and and pop the overload. Any problems with utility service?
  • mattmia2
    mattmia2 Member Posts: 2,996
    It is a resistance heater, if the voltage drops the power consumption decreases.
    PC7060
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,141
    I still think it’s Lunar. When is the full moon?
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • PC7060
    PC7060 Member Posts: 317
    edited January 16
    mattmia2 said:

    It is a resistance heater, if the voltage drops the power consumption decreases.

    Dooh! right, not a motor. :#
  • hot_rod
    hot_rod Member Posts: 14,786
    I thought of voltage issues also, but the control is basic silver points enabled by the snap disc, not sure that current would have any effect on the thermal disc? Almost need to catch it in the act, quickly measure some things, like temperatures.
    Some of the clamp on Amprobes capture high current draw conditions.
    But so do circuit breakers :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 1,292
    Is it exactly 1 month or is it every 28 days? hmmm
  • HomerJSmith
    HomerJSmith Member Posts: 1,292
    Replacing the elements and thermostats is cheap. You can buy the kit at Home Depot for peanuts. Well, not literally for peanuts.

    If you aren't experiencing any other electrical problems in the building, I would think it isn't electrical. Your service provider's engineering dept might be able to help you.

    I assume that you are not getting any seriously hot water out of the taps, so it isn't over temp related.

    "There are strange things done in the midnight sun", where water heaters toil, and fail to work, a monthly quirk, that drives men insane.
  • PC7060
    PC7060 Member Posts: 317
    "There are strange things done in the midnight sun", where water heaters toil, and fail to work, a monthly quirk, that drives men insane.
     :D:D:D
  • mattmia2
    mattmia2 Member Posts: 2,996


    I assume that you are not getting any seriously hot water out of the taps, so it isn't over temp related.

    Unless there is a thermostatic mixing valve.
  • HomerJSmith
    HomerJSmith Member Posts: 1,292
    edited January 17
    mattmia2, Good point! Yes, you are correct. I guess we should ask.
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