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float-type lwco bad?

a2shutt Member Posts: 97
how do I tell if my float style lwco is bad? A few weeks ago the manual reset was tripped on my electronic lwco (backup, I assume?). I was talking to the company who installed the boiler today and he told me about how the last boiler in this building went bad...someone didn't maintain the lwco, and it plugged up and the boiler ran dry and cracked. Since then I'm wondering if my float lwco could maybe be bad, and if so, how do I check that? Don't really want to ruin this boiler.

Also-how much water should I flush through the lwco on my monthly flush?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Preventing dry-firing

    On the usual m-m float type lwco, the weekly, or monthly flush into a bucket will clear the float-chamber of any sediment which could prevent the float from moving downwards in a low-water situation and turning off the burner.

    Many medium-sized boilers also have a backup lwco, which detects the waterline electrically, but even these need yearly, or semiannual dismantling and cleaning.

    Underneath the float type is a ball valve which drains the float chamber washing out all the sludge from a century old system. During this emptying, the burner will go off, so try to do the flush when it is running. If it does not go off when flushing until the discharge runs clear, there is something wrong with the lwco, and the system should be turned off, until a qualified tech can find the problem, and correct it. These can be rebuilt, even by yourself, but most pros advise a replacement.--NBC
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,846
    You must be missing the sticker.

    There should be a yellow sticker or tag attached to your boiler that says to blow down the low-water cutoff at least once weekly while the boiler is operating to make sure that the burner cuts out. If it doesn't you're supposed to shut the burner off and inspect the control and not turn it back on until normal operation has been restored.

    The rule of thumb is to flush until the water runs clear, but if there's a good head of steam it can be hard to tell because you can't see the water through all the steam. When I had one of these controls I'd flush it until the burners cut out, then repeat as many times as necessary until the initial stream of water looked clean. Then I'd refill the boiler to about 3/8" below the water line, because that's about where the level usually is while there is steam and condensate in the lines and radiators.

    If the installer didn't leave you a copy of the manual, you can get it here: http://completewatersystems.com/wp-content/uploads/2011/05/1427.pdf
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • a2shutt
    a2shutt Member Posts: 97

    thanks for both replies. I'll be working there on monday, and I'll do that.

    What do I need to do to maintain the electronic lwco?
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,846
    Probe-type lwco maintenance

    Just take out the probe and clean it at the end of each heating season--or more often if your boiler water is especially cruddy.

    If you're considering replacing the float-type with a probe-type, read up on them first. There are a lot of people here who don't like the ones with intermittent level tests. I don't happen to be one of them, but they're all probably smarter than me and definitely more experienced. I just went with the one the boiler manufacturer recommended.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • a2shutt
    a2shutt Member Posts: 97

    I opened the lwco valve while the boiler was running and it immediately shut down. Water ran clear in a very short period of time. Looks like we're good!

    Thanks for your replies.
  • RJ_4
    RJ_4 Member Posts: 484

    mmiller lwco should be taken apart and cleaned out by a professioal every 1 to 2 yrs depending the type of water in your area. I recommend cleaning or replacing the strainer basket assy. at least once a year, If not every 6 months.  see Mcdonnell Miller parts breakdown ( sa-101 )
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