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Boiler Cycling

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DK_5
DK_5 Member Posts: 18
in THE MAIN WALL
Thanks Long Beach Ed
I measured all the radiators and used Dan's formula on page 75 of "The Lost Art of Steam Heat" as well as Weil-McLain's boiler replacement guide. The SGO-4 is rated 144MBH DOE heating capacity and 108MBH Net I-B-R for steam. I also have a boiler mate for hot water. So it is ok for the boiler to shut down even though the set temp has not been reached?The temp eventually goes above the set limit. Just for more info, the thermostat's swing is set at four. Any more thoughts?

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  • DK_5
    DK_5 Member Posts: 18
    Boiler Cycling

    I had a new steam boiler installed in August
    Weil-McLain SGO-4 I calculated the mbh at 113,000 for my home. I have a LUX T-500 thermostat set to go down to 58 at night and up to 64 in the AM. The boiler runs about 30-35 minutes until it stops(thermostat usually at 62 or 63) then cycles on again for a few minutes. Is this normal ? I do not recall my old boiler doing this(also a WM same size).
    Pressurtrol all the way down, radiators all hot, Gorton #2 on long main, #1 on shorter main both on 6 inch nipples. Was the boiler sized too big? What should I do/try next.
  • Goober
    Goober Member Posts: 3
    Sounds good...

    What it sounds like is happening is that the boiler is shutting off on pressure. Once all the radiators are filled with steam, all the air is out of them and all the vents close, steam pressure begins to build up in the system.

    Since everything's hot, what is the sense of running the boiler further? So the pressuretrol shuts the boiler. As the steam condenses, the pressure drops and the boiler restarts.

    That's how it's supposed to work.

    Now, is the boiler too big?

    If it was replaced an old one of the same size, it very well may be. Did the installer measure all the radiators in the house? If not, I'll bet my hat that it's too big.

    A 113,000 BTH boiler would probably heat upwards of a 4,000 square foot house, but, as I said, it depends ENTIRELY on the size of the radiators installed on the system.

    Long Beach Ed
  • Gene_3
    Gene_3 Member Posts: 289
    your over thinking it

    the burner runs to make steam, not when the tstat is calling, once the steam is up, it's burner off, the heat is in the steam, think of it as coasting down the hill, if the pressure drops the burner will come back on, it may be coming on just as your tstat is shutting down, which accounts for the short time on
  • DK_5
    DK_5 Member Posts: 18


    Thanks I appreciate the input
  • Jim_64
    Jim_64 Member Posts: 253


    I have the same issue ( boiler cycling on pressure with vaporstat set to cut out at 16 oz and cut in at 6 oz and multiple Gorton #2s on my long mains ), but have a larger system 1250 sq ft of steam and a large house to heat ( 5000 sq ft ).

    The heat does get to the radiators before the boiler stops, but the downtime is about a minute or less and then it restarts. This cycle happens multiple times ( 7-10 times ) and then finally the house will be warmed up enough to satisfy the thermostat. While this does end up heating my house comfortably, the boiler's glass looks pretty sooty, so I'm unclear whether this type of operation is good for the boiler.

    Does this sound normal? Is the boiler cycling on pressure too fast / should the pressure be maintained for longer than a minute?

    Any help would be greatly appreciated.

    Thanks,
    Diar
  • Jim_64
    Jim_64 Member Posts: 253


    In my case, about 2/3 of the radiators have filled with steam when the boiler initially cuts out. The problem is that the radiators that are not filled all the way take many cycles to get completely filled, so that thermostat doesn't get satisfied quick enough.

    Does somebody know whether large systems ( 1250 sq ft steam with a 5000 sq ft wide house ) require more pressure than 16 oz to fill the system?

    Thanks again,
    Diar

  • Long Beach Ed
    Long Beach Ed Member Posts: 1,806
    Shouldn't be...

    The entire system should be filled with steam before the boiler shuts off on pressure, that is if the thermostat is not turning it off...

    If the pressure is building up that high before all the radiators are filled, you have some venting issues. Assuming this is one-pipe steam, are the ends of the mains properly vented? Have the radiator vents been replaced since Hoover was president?

    The radiators should be hot all across before the vents close and steam pressure builds.

    Lone Beach Ed
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