Weil McLane boiler keeps shutting off, pressure too high

Discussion in 'Boiler Forum' started by jralphc, Nov 14, 2013.

  1. jralphc

    jralphc New Member

    Messages:
    2
    Location:
    Lansing, Michigan
    We bought a very old house that has 30 yr. old Weil McLane boiler for steam heat. Recently we have had an issue with the boiler shutting off because the pressure is too high. If I open the drain valve and let water out of the boiler until the system starts adding water back in to the boiler it will come back on and the pressure will start to drop back to normal. But eventually this will happen again; sometimes it will operate fine for a week or more and other times it will turn off again shortly after it re-started - it is definitely an intermittent problem. What could cause this to happen?
  2. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,075
    Location:
    Maine
    The pig tail from the boiler or low water cutoff to the pressurtrol is plugged with crap. You need to remove the pressuretrol and clean it out. I assume you are blowing down the low water cutoff at least twice a month also.
  3. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    disclaimer: I am not a boiler expert. That being said, it sounds like a possible aquastat (temperature control) or part of the water pressure, water level controller. You did not mention what the water temperature or other gauges might be indicating.
    In any case, Boilers can be very dangerous, so get an expert there to diagnose and fix it, is my best and sincere advice.
  4. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,075
    Location:
    Maine
    Its a steam system. The water temperature is 212 all the time it is making heat. If its making hot water it would have a low limit aquastat on it that would maintain about 160 degrees but it would not cause his issue. Water level is controlled either manually or with an automatic water feeder like a McDonald Miller 101 that feeds water when the low water cutoff float drops. His issue is with the pressure-trol, most likely a honeywel Pa404A and more specifically with the pig tail tube that connects it to the boiler.
  5. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    OK, I said I was not an expert:), and I never worked on a steam boiler. Is that pigtail a homeowner maintenance item, or should a boiler tech service it?:confused:
  6. hboogz

    hboogz Member

    Messages:
    40
    Location:
    New York
    Removing that pigtail just requires a few turns from a channel-lock and a rag, so as to not bend/scratch the pipe ? The pigtail tube on my WM boiler is smooth, so curious if you would have to open up the side panel to get access to a threaded connection?
  7. hboogz

    hboogz Member

    Messages:
    40
    Location:
    New York
    I'm not a boiler expert either. But when you find that your boiler shuts off, are you seeing the sight glass filled with water ? I had a similar issue happen a few weeks ago and decided to change both the low-water cutoff (probe type) and automatic water feeder (both mcdonnel miller) and haven't had an issue since (Although, I'd very much like to clean out the pigtail referenced in my post above)
  8. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,075
    Location:
    Maine
    They are 1/4" npt so you can usually back them off by hand.
  9. jralphc

    jralphc New Member

    Messages:
    2
    Location:
    Lansing, Michigan
    Thanks to all of you for your suggestions and expertise. I've made an appointment for next Monday to have this taken care of, it is doing it more frequently now. It's great to have some idea about what the problem might be.
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