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Gas flue back pressure at start-up in Massachusetts

I have a Smith model 28A boiler that has just been converted from oil to a Powerflame modulated gas burner.  The boiler specs are for no draft control.  Massachusetts gas code specified the need for a spill switch, which means we must have a draft control.  The problem is that after a long shut off period, especially since we now use a very low burn rate after steam is generated, that when the burner comes on, occasionally the spill switch is activated which shuts down the system.

I checked with the chimney company and they said the chimney and draft is fine.  The problem is simply that the chimney is cold and the flue is long.  Has anyone ever heard of getting an exception to the use of the spill switch?  Any suggestions?  The problem is very intermittent, but that is a big problem, anyway.


Steve Garson

Boston, MA
Steve from Denver, CO


  • gennady
    gennady Member Posts: 839
    edited December 2011

    In gas fired boilers with barometric draft regulator, damper must swing both ways and spill switched mounted on the bottom of the damper. No way you can get rid of the spill switch. you can install motorized damper down flow of draft regulator, along with proof of opening and filing with authorities having jurisdiction. BTW, is it teflon on gas pipe tread?
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Draft over fire?

    The barometric maintains pressure in the flue downstream the barometric.

    The burner motor and air intake damper controls over fire draft.

    Power flame is a very good burner, do you have a model? I can look it up easier that way.
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