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really trust a lwco?

Hollis Member Posts: 105
How often do they fail?

Seems like a very big disaster if they do.

I wonder in this day of electronics that there isn't a second fail safe gizmo that shuts down the power if the boiler goes beyond a certain temperature when there is no water in the unit?

What is the best way of testing a probe type LWCO? Draining the boiler until it goes below the lever of the probe?


  • Unknown
    edited May 2010

    Excellent question!

    Typically the "test button" is used,,,, but the ONLY WAY to be sure is what you already described! ;-)

    Be SURE there are NO VALVES BETWEEN the boiler LWCO & system side so it cannot be isolated, usually I want 2 of them, far apart, but connected in series to be sure!
  • Jamie Hall
    Jamie Hall Member Posts: 23,280
    Belt and braces

    my boiler (which is being replaced, but not because of a low water problem!) has two, and the new one will too -- a "regular" one, tied into the auto fill valve, and a lower one, which has a manual reset.  I like that system.  And they are both tested when I blow them down.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Al Letellier_21
    Al Letellier_21 Member Posts: 402
    edited May 2010
    trusting lwco

    One, two or even three lwco's on a boiler is still no guarentee that they will work....if they are not properly maintained. Electronic probes get dirty just like a float type will....you have to pull and clean those probes as part of the annual maintenance. Have seen many a cracked or cooked steamer in my insurance work with electronic probe type lwco's.......ground out that probe and the boiler keeps on steaming till something let's go.

    Don't get too fat, dumb and happy thinking  lwco maintenance is a thing of the past...it WILL come back to haunt you !!!!

    Hint: to make removal easier, leave enough slack in your wiring and use Never Seize as your pipe dope....never teflon tape....they come out with very little effort.
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,202
    Mine Failed

    You would think that a steam man with rental properties wouldn't have these problems. 

    Last winter both low water cutoffs on one boiler failed.  I looked in on the boiler and it was firing with no water in the sight glass. 

    Both units were mechanical ones.  I don't trust electronic.  One was a McDonnell MIller #69 which threads into the back of the boiler. It has a large float contained in a cage.  Mung had built up around the float and held it up. 

    The other unit was a McDonnell MIller #47-2 cutoff/feeder.  I had the feed water turned off, as I check on the water level every week and check the controls.   The switch in this unit had failed closed.   Had the feed water been turned on,  the unit would have protected the boiler by maintaining a safe water line.  

    The experience forced some soul searching.  McDonnell Miller used to have a saying, "Hasn't it earned its retirement?"   Since their controls were so well made that they lasted virtually forever, owners seldom bothered replacing them.  I was guilty of this.  Both controls were probably 30 years old and should have been replaced 15 years ago.  All the equipment is being replaced now. 

    Each control will be wired so it can be tested separately.  Because both controls were wired in series, there was no easy way to check the #69 cutoff. 

    The new boiler will have another #47-2 and an electronic probe.  The probe will be higher than the mechanical unit. 

    And I'll leave the feed water turned on and be more diligent with my inspections. 
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