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WeilMclain SGO5 steam boiler turning on and off often.....Need Advice

MCarp Member Posts: 8
I have a customer that I just serviced.....while I replaced the nfs and got the unit running, she had told me her boiler was never turning off. I ran the unit to see that 3 of her radiator vents just kept letting out steam so I replaced them. One of the radiators was banging so, I had lifted the pipe and radiator so that it had pitch. I thought I had done well, but then a day later she was complaining that she can not sleep at night as it turns on and off often. I saw for myself that it gained pressure 3 lbs. within 10 minutes, then turned off and turned back again quickly, within 5 minutes. The customer has all the radiators off on the third floor as she does not use them so this boiler is only supplying 5 radaitors on first floor. I was told by someone who has been in the business a long time to down fire the boiler as it is a 5 section boiler and it is designed to heat the whole house and all radiators. It burns with a QB 180 oil burner with a 1.10 at 150 psi. so I'm pretty sure that would be about 1.25. It calls for 1.45 max. I'm kinda confused.....maybe I'm second guessing myself.


  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    It sounds like...

    That boiler is somewhat (maybe a lot) bigger than it needs to be for the load that's being put on it..  The oil rate works out to an EDR of somewhere around 600; even a really big radiator is not likely to be much over an EDR of 50 or 60 -- so it may be as much as twice as much boiler as is needed.

    First thing to do is to figure the size of the radiators (EDR).  From that one can figure the BTU requirement, and from there we can get to the required firing rate -- or boiler size.  I'm not sure whether that boiler can be down fired much; I am not a burner vs. boiler expert.  Down firing is what is going to be needed, though.

    In the meantime, make sure the pressure isn't too high -- 2 psi cutout is higher than really needed; 1.5 would probably be better -- and make sure that there are vents on the mains, so that the air can get out as fast as possible without depending on the radiator vents to do it.  That will help, but it won't cure the problem.

    If you post the EDR numbers here on the board, someone will be right along with a recommended firing rate to start at -- if you can get down that far.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Try a few simple

    things before resetting the firing rate.

    Make sure the pressure control is working right, and maybe try a larger differential to increase the off time.

    Also, check the thermostat and its location. If the thermostat is in an area no longer heated, then it will never stop sending demand to the boiler.
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