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Replace LWCO or do I have bigger electrical issues?

Taylor_4
Taylor_4 Member Posts: 55
in Thermostats and Controls
Have a McDonnell-Miller LWCO on my steam boiler. Blew out a couple of years ago (a lot of buzzing, then eventually it died). Antique 24V transformer suspected (but it's been a busy couple of years, so no replacement). Buzzing started on replacement LWCO a few days ago. Plumber won't replace without wiring updated, so replaced transformer and cloth wire. Now the LWCO just buzzes and won't do anything. Multimeter tells me 26V at the (new) transformer. Is this within tolerance, or do I have an electrical issue? Is the LWCO just toast from the old transformer, or do I have bigger issues? Obviously will try to get an electrician and a plumber lined up tomorrow, logistically easier if I only have to get in a plumber. Opinions?

Comments

  • JUGHNE
    JUGHNE Member Posts: 11,267
    What number of LWCO? And maybe go to the Strictly Steam part of the site.
  • Taylor_4
    Taylor_4 Member Posts: 55
    PS-802.

    Thanks, I will repost on the steam side.
  • Taylor_4
    Taylor_4 Member Posts: 55
    When I turn on power and the LWCO should be starting the burner (but just sits there buzzing), the voltage stays at 26V.

    This all started when I cut power to clean out the sight glass. When I turned power back on, it buzzed a while before starting. For a couple of weeks, intermittent buzzing when it started the burner. This afternoon, after replacing the transformer and turning the power back on, all it does is buzz.
  • Taylor_4
    Taylor_4 Member Posts: 55
    Not sure this is relevant, but just in case: The wire I replaced had 4 wires: yellow and blue used as neutral (C, I guess), red and white as hot (R, I guess). I just put in 18AWG, one red wire and one white wire, since that's all that is on the other side of the shut-off switch they go into.

    There is still some spliced-together wiring from the LWCO to the thermostat, I'm reluctant to replace that wiring now in case I get a plumber at short notice, but the replacement wire has already been fished.
  • BobC
    BobC Member Posts: 5,501
    is the LWCO itself buzzing or is it a water feeder that the LWCO controls that is buzzing?

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Taylor_4
    Taylor_4 Member Posts: 55
    There is no water feeder right now. It is the LWCO. Does this have an internal transformer that might be failing?
  • JUGHNE
    JUGHNE Member Posts: 11,267
    What VA rating of transformer do you have and is this LWCO married to a water feeder? Has the probe been cleaned recently..some one will have an answer...I don't see many of these. But the steam site guys do.
  • Taylor_4
    Taylor_4 Member Posts: 55
    Honeywell AT140A, 40VA.

    There is no water feeder.

    The probe has not been cleaned since it was installed.
  • BobC
    BobC Member Posts: 5,501
    Some LWCO do have internal transformers, what model number is this?

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Taylor_4
    Taylor_4 Member Posts: 55
    PS-802.

    Good to know the new transformer is not the problem.
  • Fred
    Fred Member Posts: 8,542
    Does the probe that goes into the boiler have any teflon tape on it? Those probes have to ground to the boiler block in order to work.
    When you took the 4 wires off, were there any jumpers on any of the terminals?
    If you take the two wires off of the LWCO and hold them together or put a jumper on those 2 wires, will the boiler burner kick in?
  • Taylor_4
    Taylor_4 Member Posts: 55
    I didn't go near the LWCO itself. I only replaced the wires from the 24V transformer to the shut-off switch, and left the wires from the shut-off to the LWCO. The replaced wires had blue/green spliced with white to the LWCO, and red/white to the shut-off switch (and thence brown wire to LWCO). I'd rather let professionals mess with the controls themselves.
  • BobC
    BobC Member Posts: 5,501
    edited January 2015
    Here's the manual for that LWCO -

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Taylor_4
    Taylor_4 Member Posts: 55
    Thanks, not sure if that's my model, I think I have the manual for its predecessor. I notice that unit has a pilot rating of 50VA. My transformer is 40VA.
  • Empire_2
    Empire_2 Member Posts: 2,340
    Where is the water level in the boiler? You said that there is no water feed valve so try to fill that boiler and see if the water level comes up. It is kind of hard to see, but give it a try if the level is lo. Is the control in alarm right now?



    Peace
    Mike T.

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