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Thread: Corroded inlet pipe to water heater and drain issues?

  1. #1
    DIY Junior Member snetsie's Avatar
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    Feb 2012
    Suwanee, GA

    Default Corroded inlet pipe to water heater and drain issues?

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    GE SmartWater Heater Model #GG40T6A guessing as old as when I purchased home 13 years ago. Cold water pipe going into heater should be black but is corroded quite badly. After reading forums here and elsewhere, wondering what is best option: replace pipe if possible? or entire water heater and what about correct draining - use expansion tank (what's it's purose vs. valve on top of tank). I do have a PVC drain pipe nearby from AC unit (see pic) I could possibly feed into?
    House is almost 20 yrs. old and needs many other improvements, current market value guessing about $120K. What'll be best investment for intention to sell house in 3 years without going overboard? Then again might look to possibly rent it in a few years as oppose to selling it... Your expertise would be greatly appreciated. Thank you!

  2. #2
    In the Trades Gary Swart's Avatar
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    Sep 2004
    Yakima WA


    Lots of good questions here. Although the tank is pretty old, there is no point replacing it until it begins to leak, and it could last for years. Unless local/state codes require solid connections, the easiest way to connect water lines is with flex copper. If those are black iron nipples, they should not have been used in the first place. replace with brass then the copper flex to the shut off valves. The valve on the top of the tank is call a Temperature/Pressure relief valve (T/P). Its purpose is to open if either the temperature or the pressure inside the heater gets too high. Without this valve, the tank can literally explode. A thermal expansion tank is sort of related to the T/P, but may or may not be needed in your home. When your water heater kicks on and heats water, this causes expansion. Water does not compress, so this expansion has to go somewhere. In many homes, this expansion is absorbed by the city water main. However, it is becoming increasingly common for the city water pressure to be too high. (above 80 psi) To control this, a Pressure Reducing Valve (PRV) is installed. Inside this PRV is a check valve which prevents the expansion from passing into the city main. This in turn causes the pressure in the water heater to rise quickly and dramatically. Sometimes a faulty toilet fill valve will open are relieve the pressure, but otherwise it is the T/P that opens to handle the expansion. It is not a huge amount of water that is released, but it still can cause a mess. Also, sometimes the T/P gets corroded a bit and will not close tightly after the pressure is relieved. This can be a big problem. The solutions for this is a thermal expansion tank that is placed in the cold water supply line between the water heater and the PRV. It should be noted that some new water meters now have a check valve built in to assure that water from the home can not get back into the supply, and some newer PRVs have a bypass to allow expansion to bypass. Most of them, a PRV means you need an expansion tank. I notice the pipe from the T/P is just a short length of PVC. This pipe is supposed to be either CPVC, copper or steel and be elbowed down to about 6" from the floor. It can not be plumbed solidly into a drain. A floor drain is ideal for this drain. It might be possible to use that AC drain, but I'm not clear on just how that could be connected. Neither the heater nor the AC should be solidly plumbed into a drain.
    Last edited by Terry; 02-13-2012 at 06:05 PM.

  3. #3
    DIY Senior Member JerryR's Avatar
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    Jul 2011


    The corrosion was caused by dissimilar metal contact.

    The norm is not to directly connect the copper pipe to the nipple at the water heater as yours is connected, without some dielectric protection. This can be either a dielectric union or a special dielectric nipple off the

    Do a google search for "dielectric union".

    My water heater has CPVC as your does off the T&P valve, except it goes out the block wall and exits outside. My wh is installed in the garage that is at street level, no basement.


  4. #4
    DIY Senior Member kreemoweet's Avatar
    Join Date
    Sep 2009
    Seattle. WA


    More than likely, the extreme corrosion shown is a result of some very ignorant person attaching plain steel pipe nipples to the
    WH. It has nothing to do with dissimilar metal contact. The unrusted steel nipple looks very new, but will be looking like the other one
    in short order. Just about any flexible water heater connecter is inherently "dielectric", so no special device is needed. The pressure relief
    valve outlet should be plumbed to the outdoors or to an interior drain; if that is not possible, the outlet should be plain pipe/tubing (no threads),
    and should terminate no higher than six inches above the floor. Plastic pipe should not be connected within 24 inches of the WH.

  5. #5
    Join Date
    Jan 2010
    Blog Entries


    Post the serial number and I'll tell you when the heater was built.

  6. #6
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    The black iron pipes are corroding inside, even the one which looks OK on the outside, and putting rust in your water. All that needs to be replaced with brass.

    Looks like a plastic pipe coming off the relieve valve....BAD!

  7. #7
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona


    Any time a black steel pipe is used on fresh water it is going to corrode. But it has to get wet to do it, so that cold water connection had to be leaking for a long time. the plastic line from the relief valve does not satisfy the "full sized opening" requirement, but many areas allow it as long as it is CPVC which that one is. But, it must NOT discharge horizontally.
    Licensed residential and commercial plumber

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