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Boil zones

J.C.A._3 Member Posts: 2,981


  • Steve Madden
    Steve Madden Member Posts: 1
    Boiler zones

    I installed Oil fired boiler with two zones. It was direct replacement. Both zones are piping into the bottom of the boiler in the return with a circulator on each zone. The circulators are powered by line voltage thermostats.

    One zone constantly comes back cold. When I start up the system and bleed that zone. That zone stays hot for about 6 to 8 hours before going cold. Then needs to be bleed to hold temperature.

    What could be the problem.
  • Brad White_135
    Brad White_135 Member Posts: 16
    Pumping Away

    A Mantra on this site... New to everyone at one point or another...

    All circulators should be located just downstream of the system expansion tank, wherever that happens to be.

    (Most often, but not always, it is located on the discharge of the boiler where there may be an air separator. A convenient place to connect the expansion tank, that is why.)

    In your situation, you are probably pumping TO your expansion tank. What happens is that the total pressure your pump creates is almost entirely negative pressure on the suction side of your pump. This draws in air from any gaps, automatic air vents are the usual suspects.

    Move the expansion tank connection point to the suction side of the pumps and see things improve once vented again.

    As a stop-gap measure, buy an expansion tank and a hose connector with a 1/2" FPT adapter. Tie the expansion tank to a drain valve if you have one, upstream of the pumps. Quickly remove and plug the existing expansion tank connection.

    This will save you some cutting and show results.
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