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The case of the stuck flow switch

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RayWohlfarth
RayWohlfarth Member Posts: 2,017
edited April 17 in THE MAIN WALL

In this weeks video, I discuss a job where the boiler was moaning when firing. Turns out the flow was too low. The owner jumped the flow switch out. The video talks about how they work and what service they require.

https://www.youtube.com/watch?v=lnWnTMbzhaY
Ray Wohlfarth
Boiler Lessons
GGross

Comments

  • JUGHNE
    JUGHNE Member Posts: 11,591

    Familiar with flow switch on Raypac pool heater.

    The other use I have seen is for pump control.

    1961 schoolhouse has a primary circ and a secondary circ piped in parallel with flow check for each.

    It was wired in what seemed to be a unique and simple method. Maybe common but I have never seen another setup like this.

    There are 2 pumps in parallel, each has a manual toggle switch. The flow switch is in the discharge pipe of pump 1.

    You start pump 1 manually, once the NO flow switch closes (wired parallel across the manual switch #1, holding pump 1 on) you then turn the #1 switch off.

    Then turn pump switch #2 on, it is wired parallel across the other set of contacts (NC) in the flow switch, which is now open. Pump #2 will not run until flow stops from pump #1. A pilot light is connected to pump #2 so you are aware the #1 failed.

    This is not for boiler protection as the boiler is a Kewanee with temp controls.

    Has anyone else seen this set up? I thought it was of interest.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 20,378

    @JUGHNE

    Never seen it done quite that way. I have seen systems where you run one pump and if it fails it's wired to bring on the 2d pump automatically.

  • RayWohlfarth
    RayWohlfarth Member Posts: 2,017

    @JUGHNE Never saw one done like that Wonder what the reasoning was

    Ray Wohlfarth
    Boiler Lessons
  • JUGHNE
    JUGHNE Member Posts: 11,591

    This was an economical way to provide auto pump change over. The flow switch was the only added component for the pump wiring. Years later someone added an outdoor tstat to keep the pumps off during mild weather of 45+ degrees.

    Weak point was that, for this wiring method, both pumps had to be on the same circuit. Each did have a SSU fustat though.

    The reason for this setup was that they wanted to insure water flow thru the system.

    No glyco, just water. Emitters on outside walls under massive windows. Supply lines in ceiling with flat roof. 1961 R-value everywhere. Fan coils with outside air.

    Powers pneumatic controls for entire building.

    Original air compressor, original B&G 1/2HP pump motors. Same compression air tank hanging, original boiler tubing.

  • Fitzy_Fitta
    Fitzy_Fitta Member Posts: 7

    I smoked a lochinvar copper fin tube boiler when I was a younger green apprentice. The nursing home had 2 lochinvar boilers feeding a water source heat pump loop. Primary/secondary loop with 3-way injection valve for the heat pumps. Boiler kept tripping the high limit. I was rushing to get the boiler running because the loop temp was too low wirh just 1 boiler in mid February. I found the pump starter had tripped. I reset it and put the pump in hand. I heard a swoosh noise and water flowing out of the burner section. I called my service manager in a panic. A quick conversation and I told the maintenance guy the problem was a faulty heat exchanger. We ended up replacing the whole boiler and I learned a valuable lesson. Never jump out a safety. That heat exchanger was smoking hot. I reset the boiler probably a half dozen times before I sent it to the scrap yard when putting that pump in hand mode.

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