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Thread: Weil McLane boiler keeps shutting off, pressure too high

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    DIY Junior Member jralphc's Avatar
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    Default Weil McLane boiler keeps shutting off, pressure too high

    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?

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    In the Trades Tom Sawyer's Avatar
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    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.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by jralphc View Post
    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?
    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.
    I am definitely not a pro plumber, but I am a pro crastinator

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    In the Trades Tom Sawyer's Avatar
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    Quote Originally Posted by BobL43 View Post
    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.
    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.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    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.
    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?
    I am definitely not a pro plumber, but I am a pro crastinator

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    DIY Member hboogz's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    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.
    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?

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    DIY Member hboogz's Avatar
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    Quote Originally Posted by jralphc View Post
    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?
    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)

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    In the Trades Tom Sawyer's Avatar
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    Quote Originally Posted by hboogz View Post
    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?
    They are 1/4" npt so you can usually back them off by hand.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member jralphc's Avatar
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    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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