Corroding Dielectric Union

Discussion in 'Water Heaters and Softeners' started by Noahboa, Jun 10, 2013.

  1. Jun 10, 2013 #1

    Noahboa

    Noahboa

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    I recently installed a Whirlpool hot water heater (Model No. ND50T122-403) in my home. I connected the water heater to the copper piping in my home using dielectric unions. Within a week or two of installing the water heater I noticed that I would get a burst of brown rust colored water the first time I used the hot water heater after it had sat overnight or while I was away at work. When I disconnected the dielectric unions I could see rust on the galvanized nipple of the dielectric union (see photos). I tried replacing the unions and made sure that I did not over tighten them to ensure that there would not be any inadvertent contact between the dissimilar metals. This did not help and I started noticing the brown rust colored water within days of installing the new unions. When I drain water from the tank at the spigot at the bottom of the tank the water is clear.

    Does anyone have any ideas as to what might be causing the corrosion and what I may be able to do to correct the issue? Thanks in advance for your help.

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  2. Jun 11, 2013 #2

    Caduceus

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    Try to give us very accurate timeline of the new installation and experiences with the old tank that was replaced. The details are important, because there may be a catalyst causing premature corrosion of your tank. Are you on well or city water? Do you have a softener? How hot do you set your tank? Stuff like that may help us.
    If you run your water for a bit and the rust starts, it sounds like the tank body is corroded inside. Just rusting in the nipples usually doesn't show much in what comes out of the faucet.
    Shutting the water down during the tank/union change and turning it back on may cause discoloration from the backwash in the pipes, but that goes away soon. Also, if you run the hot water for 5 minutes straight, is the water coming out rusty the whole time or just in the beginning?
    Even some photos of the surrounding area and connected piping for the new install may help. Please understand this can be a tricky thing to diagnose without being there.
     
  3. Jun 11, 2013 #3

    Noahboa

    Noahboa

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    Caduceus,

    I first noticed the brown water approximately 1.5 to 2 weeks after the installation. I did experience a similar problem with my old tank but this was only after it sat unused for a week or more when we were gone on vacation. With the new tank it only has to sit overnight before I observe the brown water. The water is only brown for a short while after I turn on the hot water. Maybe 1-2 seconds after it has sat for roughly 8 hours. I have city water and no softener. My tank is set to 120 deg F. I don't observe any brown water when using just the cold water. I have attached a few photos of the heater. Thanks for your help.

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  4. Jun 12, 2013 #4

    Caduceus

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    From what you have told me I am more enclined to believe the problem is in your pipes and not the tank. If you can try a few tests, they may help to solve this mystery. First, shut the cold water supply to the tank off. Be careful not to scald yourself and open the T&P valve (temperature and pressure) on the upper right part of your tank with a clean bucket at the end to retrieve some water. Only let it out for a few seconds and click the valve closed. See if the water is rusty. With the cold water still off, open the boiler drain at the bottom of the tank, with a hose attached to it and do the same to see if the water is rusty.
    I'm thinking that there is a possibility that there are either old steel pipes or old valves, maybe both, on the hot water system and that is causing the rusty water to develop. If there is a dead ended pipe or an unused branch of pipings, the rust will collect and when you turn the water on it gets flushed out.
    Try what I've recommended and look around at the piping in the house and see if you can find anything like the circumstances that I've described.
     
  5. Jun 13, 2013 #5

    Noahboa

    Noahboa

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    When I drain water from the tank, it comes out clear and not rust colored. If my problem is due to rust in my pipes there are two issues which I don't feel it explains. First, why would the condition have become so much worse after installing the new water heater and secondly how would this explain the corrosion I observe on the dielectric unions?
     
  6. Jun 13, 2013 #6

    havasu

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    I would recommend a different type of dielectric union (the ones I use are about 4" tall and are made from a stainless steel material) but that would be alot of work which would including cutting and soldering.
     
  7. Jun 13, 2013 #7

    johnjh2o

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    May not have anything to do with your problem but what are the water lines at the bottom of the heater? One of them appears to have a galvanized union connected to it.
     
  8. Jun 14, 2013 #8

    Noahboa

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    Havasu - I have checked two different hardware stores and the only dielectric unions they had are the ones I installed. Do you have to go to a plumbing retailer to find the ones you refer to?

    johnjh20 - The water lines at the bottom of the water heater are copper. I think what you are seeing is the gas line which runs in front of the water lines.

    Is it possible that there is a short somewhere within the water heater that is driving the corrosion of the dielectric unions? Is it likely that replacing the water heater will solve the problem?

    Thanks.
     
  9. Jun 14, 2013 #9

    havasu

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    The dielectric unions I purchase come from either Lowe's or Home Depot's big box store. Remember though, I am just a handyman and not an expert like John, Phish or Cad.
     
  10. Jun 15, 2013 #10

    camaroderrick73

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    New water heater do not rust out in 2 weeks. The water lines look installed properly to me. The test you did tells me that the water heater is not the issue. Now here in ca we normally use stainless water flexes (24 inches) to attach the copper the the galvi nipples.
     
  11. Jun 15, 2013 #11

    camaroderrick73

    camaroderrick73

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    Also new water heater should come with dialetric heat trap nipples. Which have plastic inside them.

    In a side note ; is this a power dampner water heater? I just ran into these and I really like the technology behind them.
     
  12. Jun 16, 2013 #12

    Caduceus

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    The supply nipples that havasu referred to are galvanized hot/cold. It does look as though the interior of the nipples on your tank are not galvanized (zinc coated). Don't let this distract you from my earlier post that there may be a water line issue trapping a small volume of rusty water caused by old plumbing. It has already been ruled-out that the tank is the problem. Look into into the possibilities that I have mentioned before, such as old valved off lines or steel piping.
    Added: I've been busy with a project at work and apologize for not being attentive to the thread.
     
    Last edited: Jun 16, 2013
  13. Jun 22, 2013 #13

    Noahboa

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    Ok so after doing a little more investigation I determined that there appears to be a stray current in the system. First I disconnected the water pipes from the hot water heater and I unplugged it (It relies on an electrical power source to open and close an exhaust vent). Then I stuck one lead of my multimeter in the water of the hot water tank and touched the other lead to ground the voltage reads approximately 1.1 volts DC. If I then disconnect the gas line as well, the voltage drops to 0.65 volts. After the electric, water and gas lines have been disconnected the water heater should be completely isolated so I am not sure how I am still getting a stray current. I am almost certain at this point that the corrosion has to be related to stray current. Does anyone have any suggestions as to what may be causing the stray current. Thanks.
     
  14. Oct 6, 2013 #14

    robmcg

    robmcg

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    Something is obviously causing the current. Have u had an electrician out to look. It could be simple as a telephone wire grounded somewhere
     
  15. Oct 6, 2013 #15

    robmcg

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    Or even an ungrounded or faulty appliance ie:d\w washing machine. Bottom line. Electric current will cause corrosion which will cause rust which it is somehow doing in urs. Is it at every faucet?
     
  16. Dec 12, 2013 #16

    Plumbingandwatertreatment

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    Get rid of the dielectrics and install the standard insulated nipples, that will solve your plrolem.
     

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