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Weil McLain LGB-6 steam boiler extreme short cycling

Erock7625
Erock7625 Member Posts: 7
in Strictly Steam

Hello, we have a Weil McLain LGB-6 steam boiler that heats our house. It was serviced a month ago for the heating season but seems to be acting oddly now. We have the thermostat sat at 68 most of the time which it can maintain but it never seems to be able to get above that temp if I set it a few degrees higher. Today I noticed it seems to be in an extremely short cycle loop where the burner ignites and runs for about 30-40 seconds then shuts off. About a minute later it repeats and continues to do that. The pressure appears to be around 1psi and the sight glass appears to be slightly above halfway. Is this normal operation or does it indicate a problem.

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Comments

  • KC_Jones
    KC_Jones Member Posts: 5,858

    First thing I notice is there doesn't appear to be water in the sight glass. Are you sure it has water? It could be steaming and going off on low water and shutting down immediately. Boiling water settles and it fires again, then repeats that cycle. The other possibility is the sight glass is full of water which leads to the next question.

    Does the pressure on the gauge ever go to zero?

    I don't always trust old gauges, but we need to start somewhere with diagnosis.

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • KC_Jones
    KC_Jones Member Posts: 5,858

    Also, how may square feet is the mansion you live in? That is a gigantic boiler, so my curiosity has been piqued.

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    LRCCBJ
  • Erock7625
    Erock7625 Member Posts: 7

    Yeah at first I thought there was no water as well, but I got a flashlight and can see the water level, it seemed to be above half and bouncing around a bit higher. The water is just clean and the sight gauge dirty. The low water cutoff has only a green light on. I believe it does go to zero when the boiler is off.

    Ha, not really a mansion, it's a century house that is about 4000sf, it has about 22 radiators on the 1st/2nd floor. There is a basement that is maybe 800sf that has a few ceiling mounted radiators. The boiler is under the old carriage house out back and the steam pipes run through a tunnel that connects the carriage house to the main house. The carriage house has steam radiators as well but those have been long disconnected.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,683

    If it is in a one bedroom 900 square foot rancher, then that boiler is oversized and will short cycle. No way around it.

    But seriously, where is the water level in that boiler. Can't see it in the gauge glass

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • KC_Jones
    KC_Jones Member Posts: 5,858
    edited December 2024

    The boiler is oversized, most likely massively oversized. That is unless every radiator is the size of a small truck? Disconnecting the carriage house wasn't a good idea unless the boiler was downsized accordingly. Honestly, it was probably still oversized with the carriage house connected, but that's just a guess.

    Have you lived here for a while to know this is a new problem, or is this your first year and you don't have a history?

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Erock7625
    Erock7625 Member Posts: 7

    The carriage house had 2 radiators on the first level and there is an upstairs finished space that had a few radiators, the upstairs space has been converted to use a heat pump system.

    The sight glass is about 2/3 full, it bounces around a bit higher and lower when the burner activates. Here's a better picture of it.

    20241206_122219.jpg

  • KarlW
    KarlW Member Posts: 170

    Watch a cycle, is it hitting pressure right away and shutting off at 1psi?

    If it does that it is cycling normally.

  • Erock7625
    Erock7625 Member Posts: 7

    It seems to pretty stay at around 1psi

  • Jamie Hall
    Jamie Hall Member Posts: 25,210

    Do you have a low pressure gauge? Say 0 to3 psig? Or can you put one on there? I'm suspecting a serious venting problem (main vent or vents stuck shut), but the only really reliable way to find out what's happening is a good low pressure gauge. What you are looking for is on firing, the pressure should rise, but only slightly — a few ounces at most — and then stay stable at that level, or nearly stable, until all the radiators are pretty well filled. Then the pressure will rise again and shut off the boiler.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • dabrakeman
    dabrakeman Member Posts: 653
    https://forum.heatinghelp.com/discussion/comment/1825146#Comment_1825146

    This. ^

    Need to understand whether this is a change in behavior just this season after the last servicing? If so then need a review of exactly what the service technician did.

  • neilc
    neilc Member Posts: 2,901

    the way your control and gage tree is configured, the trols may be sitting in water and gunk, I would check the trol nipples and the cross tree for gunk, and then extend the trols and gage up above the top of the inverted trap so they're above any possible water/gunk level in that tree,

    add the low pressure gage while you're at it

    known to beat dead horses

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