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Wiring a Taco LWCO to a Viessmann Vitodens 200W

RAW10000 Member Posts: 2
Hello. I am in the process of installing a LWCO to my boiler per the request of the local inspector. I have a Viessmann Vitodens 200W and I purchased a Taco LWCO device (120v, manual reset). The Viessmann manual specifies that the LWCO should cut power to the boiler (at the power source) and not merely to the burner. So far I have plumbed for the LWCO and have run a power leg to it. My plan was to wire up the LWCO more or less as a switch - in the event of a water loss, the LWCO would shut off power to the plugs that my power module and my Taco zone controllers are plugged into. Am I on the right track with this? If so, I am not quite sure of the wiring. The schematics all make reference to a burner circuit, but the problem I am having is I can't seem to figure out where to wire the hot wire for the plugs. That is to say I run the source power to the N and H terminals, and there is a jumper from the H to the COM terminal. It then indicates that the Neutral from the plug should go to the NC terminal but does not specify a location for the hot wire coming from the plug. Should this go on the H terminal? Any help would be appreciated.



  • CMadatMe
    CMadatMe Member Posts: 3,086

    LWCO is useless. It's just an ornament and will not serve any purpose except satisfy an inspector that doesn't know what he is inspecting. Boiler will never operate the burner if the flow switch doesn't open. This would require water moving at the proper flow rate.

    Wire the LWCO to shut power at the box powering the PPM.

    There was an error rendering this rich post.

  • RAW10000
    RAW10000 Member Posts: 2

    You are probably right about its effectiveness, but the inspector is driving this. I do want to wire this just as you are suggesting - to cut power to all pumps, power pump module, boiler - all at once. My issue is how to wire the Taco LWCO in order to make this happen. I wired it as I thought it should be but the test button does not cut power to the outlet I wired up (I wired it to an outlet with a lamp plugged in so that I can test proper functionality)
  • meplumber
    meplumber Member Posts: 678
    I agree to an extent Chris.

    I agree with you on principle.  However, in many jurisdictions, the internal flow switch does not satisfy the requirement for an external Low Water Cutoff device, especially if there is radiation below the boiler level.

    Having witnessed a catastrophic failure caused by an improperly wired LWCO (not a Viessamann), my faith in the contacts on the flow switch is minimal.  I will continue to install an external LWCO.  Not only because code requires it, but also for piece of mind.

    Chris's advice is correct.  Wire the LWCO to kill power to the outlet that the PPM and the Zone Controller plug into.

    Good Luck.
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