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Smith boiler, auto damper switch and override

d8734 Member Posts: 4
edited November 2022 in Strictly Steam
Hi, this fall I had a problem with my 1990s Smith natural gas steam boiler diagnosed as the automatic damper switch failing. The technician (from our local municipal utility, great service) said that the part, the auto damper switch, was no longer made, and retrofits are not great. He adjusted the damper to be always open, advised that there is some minimal efficiency loss for that fix, and said that if the boiler stops working again, to try adjusting the damper manually. Well, a month or two later, yes, the boiler stopped working again, so I adjusted the damper. Came back on, but stopped working again over night. I adjusted the damper again, and it seems to be working, for now. 

My question is, are there options for not having to constantly monitor the damper now? Is it normal to shift position on its own like this? Is there a good retrofit for this (I'm seeing whole damper systems, with switch and etc)?

Advice appreciated. Thanks! 


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,068
    edited November 2022
    Remove the damper and replace it with a short piece of galvanized pipe of the same diameter. Some minor rewiring will need to be completed. If you can take a picture of the wiring diagram and post it here I can provide you with the rewire. The diagram is usually a sticker on the door panel sometimes on the inside

    It is very IMPORTANT to remove the damper before doing the rewire. You don't want the damper closing accidentally with no safety switch in place.

    EDIT: Looked al over the web for older HB Smith boiler IO manuals that may contain the wiring diagram. I was unsuccessful. I hope you can see/find the diagram on the boiler.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    Long Beach Ed
  • d8734
    d8734 Member Posts: 4
    Thanks Ed! That makes logical sense. I may try installing a new damper and switch component that I found as a replacement, and keep this idea as a backup. A place online claims that there is a replacement damper and switch for the GB-200 boiler? It's not cheap, but I feel that if it works, it's a good investment in a machine that will probably last a few years longer. I don't see a wiring diagram. 
  • Steamhead
    Steamhead Member Posts: 16,252
    edited November 2022
    @d8734 , replace the damper with one made by Field Controls. The drive motor is replaceable on these units if it goes bad. See:


    Not only does the damper keep the boiler from cooling down so much between cycles, but by closing off the chimney opening it also reduces the amount of cold air infiltration to the house.

    I'm pretty sure the Johnson dampers (Smith put their name on Johnson dampers) used the same type of cable connection as the Field ones do.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Long Beach Ed
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 840
    I have a GB200 -S-5 boiler more than 20 years old. The manual at the time was GB200-IM-3, 42-9184. If you try to look it up all I could find today is IM-5, 42-9184. The model numbers for the vent damper are different. Additionally, A O Smith has a list of replacement parts for boilers. There are different model vent dampers for the different boiler capacities.

    I can email both the IM-3 version of the manual and the replacement parts list. Send me a message if you want them.

    While this is probably simple, someone more knowledgeable than I should help you. Personally, I would replace the vent damper, not inactivate it. Others have different views on the whys of vent dampers.

    Good luck.

  • d8734
    d8734 Member Posts: 4
    Thanks to you both! I have searched and downloaded that GB-200 manual, which includes a replacement parts list, and verified that what I found on a parts sales site is correct for my boiler (it's a GB-200-S-4L), so I've gone ahead and ordered the replacement vent damper and switch. Now that I have the wiring diagram also, in that manual, I'll see if the part looks easy enough to install on my own (could be, as Steamhead says, same electrical fitting, it looks very similar on the photo for the part), but I can also always give the utility company a call for them to install. 

    The damper, as it is now, is continuing to shut the furnace off every 12-24 hours, which is a mild pain, so I am looking forward to getting this back working optimally. Thanks for all of the advice here. 
  • d8734
    d8734 Member Posts: 4
    Update: the part arrived, it is the Field Control model, and the furnace is working again. Strangely, the rotation of the vent damper, marked on the outside, is the opposite of the original part, but that shouldn't make a difference, should it? The position of the switch and the crimping of the one end of the galvanized pipe are the same as the original, so that seemed to make sense.