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How do I find GPM on a boiler (Flow Switch Problems)

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Dairon421
Dairon421 Member Posts: 80
edited May 2021 in THE MAIN WALL
Hey I'm trying to see if the flow switch I have is defective. Its is in a apartment build and the they using 2)boilers. One boiler is for heating the building. The boiler that not working heats the hot water for the building and it uses a storage tank. It not working because of a open flow switch(SERIES FS4-3 GENERAL PURPOSE FLOW SWITCH). I tested the circulator pump and I got voltage going to it. The rated amps for the pump is 1.8 but I'm getting 2.0 amps which is not so bad. I checked if any ball valves was in the closed position but they all was open. I remove the float switch from the tee and saw no debris in the copper pipe and the paddle moves freely on the flow switch. Right now I want to verify that the flow rate is high enough for it to activate or not, but I don't know the steps to finding the flow rate.

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  • Zman
    Zman Member Posts: 7,569
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    Flow switches on DHW systems frequently go bad. They can also be a bit finicky to set up and test.
    You can verify that you have the correct flow by measuring the difference between the inlet and outlet temp on the boiler when it is at full fire. Most systems are designed for a Delta T of ~20 degrees.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,543
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    @Dairon421

    Possible that the pump motor is dragging and not moving enough flow. Try throttling a valve on the pump discharge while you amp meter is checking the pump amps. If the amps change when you operate the valve the pump is likely ok. Amps will go down as you close the valve.


    As @Zman said check the temp drop across the boiler when it is firing 100% with a load on it. High delta could be not enough flow

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