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install a LWCO in a Old gas furnace

Jsencion Member Posts: 6
Hi everyone! I'm electrician and I'm new with boiler wiring, I have a old gas furnace in a residential place, it's have few components that I made my research on internet about them, I can not figure out the a way to add a New LWCO to the Old furnace that doesn't have one, this is the wiring diagram and the brand of the LWCO to be install, is somebody can give a hand I appreciate it please


  • pecmsg
    pecmsg Member Posts: 2,894
    An Electrician cant figure this out...................

    Break the primary circuit!
  • Jamie Hall
    Jamie Hall Member Posts: 18,935
    Yeah... except that control looks like it's for 24 volts. Therefore...

    Break the gas valve circuit!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 15,331
    @Jsencion , what model Weil-McLain?

    Steam or hot-water?

    Where are you going to mount the control?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Danny Scully
    Danny Scully Member Posts: 1,334
    What good is a LWCO on a furnace…😉
  • Jsencion
    Jsencion Member Posts: 6
    @Steamhead is a Weil- mclain yes, steam. Here the picture you can see where is Mounted 
  • Jsencion
    Jsencion Member Posts: 6
    @Steamhead im sorry, hot water
  • Danny Scully
    Danny Scully Member Posts: 1,334
    Why 2 LWCO? 
  • Jsencion
    Jsencion Member Posts: 6
    @Danny Scully is just one, the other device inside is a high limit control
    EBEBRATT-Ed Member Posts: 11,998

    You need to power the LWCO with 24 volt power constant hot.. Then wire the LWCO switch in series with your high limit control shown on the diagram.

    If there is a jumper between the power contact and the switch contact in the LWCO take it out. Look at the instructions.

    Bump the relief valve on top of the LWCO to get any air out.

  • Danny Scully
    Danny Scully Member Posts: 1,334
    I wasn’t talking about the aquastat, I was talking about the 2nd LWCO.

    HVACNUT Member Posts: 4,593
    I believe that model M&M is 115v powered. Switching can be either line or low volt 
  • realliveplumber
    realliveplumber Member Posts: 58
    That round lwco is too low. It should be above the boiler, and should shut the boiler down before there is no water in the boiler.