Water Heater flow restriction

Discussion in 'Water Heater Forum, Tanks' started by kevink1955, Nov 18, 2019.

  1. kevink1955

    kevink1955 Member

    Nov 17, 2011
    L.I. New York
    Has anyone ever had a dielectric coupling (3/4 X 3/4 MPT) rust internally and restrict water flow

    I have a Larrs/Bradford White RV 75 indirect that devolved a restriction to the DWW flow. When flowing DHW you can hear a hissing noise around the HW outlet on the top of the tank so I am thinking it's in the dielectric coupling the factory so thoughtfully installed.

    There is a similar fitting on the bottom of the tank and attached to it is a combination water inlet and drain valve of a type I have never seen before. I wrote a question years ago about how to flush this heater when the cold inlet ant drain valve are in the same fitting. Opening the drain valve just flows water from the cold water line straight out the drain, nothing moves thru the tank at all.

    Need to pull a few things apart but am looking for a direction to start in.

    Thanks Kevin
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    Dielectric pipe nipples with plastic liners have never been a problem for me.
    However dielectric unions of steel have performed poorly. I don't bother installing them.
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  4. kevink1955

    kevink1955 Member

    Nov 17, 2011
    L.I. New York
    Had time to troubleshoot this today, found the HW outlet is 3/4 fpt not a 3/4 X 3/4 nipple as I originally stated.

    Removed the piping and looking straight down the outlet fitting (that apears to be welded into the top of the tank) there is a white plastic piece that appears to have a small slot in the side, I am thinking this some sort of heat trap but it is definitely my restriction (see first picture)

    I punched it out with a piece of 1/2 inch copper tubing and put the plumbing back together, problem solved.

    This is not like any heat trap I have ever seen, how they installed this is a mistery to me as the outlet fitting looks like a stainless coupling that is welded into the tank, if the plastic was in there prior to welding it would have been melted

    Anyone ever seen this before, the tank drawings I have do not show any heat trap or anode rod so I do nor know what they intended this thing to do other than clog up and slow the water flow!!

    Attached Files:

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