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  1. #1
    Join Date
    Jul 2007
    Location
    Chicago IL
    Posts
    167

    Flame rod wired to HSI neutral

    Rheem UGDG12EARJR. Mid 1990s (?). During a courtesy inspection I noticed the flame rod was wired directly to the neutral off the hot surface ignitor. I did not have a schematic available, though it looks field installed. I've never heard of this being done before. Is this common for others?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,614
    Furnace originally didn't come with a flame rod. For more reliable sensing, a kit was added in the field. Pretty rare, most brands had a separate sensor.

  3. #3
    Join Date
    Dec 2006
    Location
    DFW Texas
    Posts
    47
    Non integrated. hmmmm Learned something new.

  4. #4
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    As the Bald one pointed out, that is a field installed flame sensor kit for when there is a problem with flame sensing, it came from the factory using the HSI itself as the flame sensor.
    If the furnace has a single IFC for fan and ignition, a replacement IFC would require the remote flame sensor wired back to the board, there is a kit for it.

    Quote Originally Posted by tinmanintx View Post
    was the flame sensing rod still wired to the control board like it came from the factory? If so you have to ask yourself how does the flame sensor work and what would wiring it to neutral do? from what you describe, someone has bypassed the flame proving safety for that unit. If the HSI goes out, there is potential for that unit to dump gas because it always sees a flame. Not good.
    Those furnaces came from the factory using the HSI itself as the flame sensor. The control board looks for a rectified signal for flame sensing, so there is no danger of it dumping gas if the HSI goes out.
    If more government is the answer, then it's a really stupid question.

  5. #5
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,653
    Quote Originally Posted by tinmanintx View Post
    was the flame sensing rod still wired to the control board like it came from the factory? If so you have to ask yourself how does the flame sensor work and what would wiring it to neutral do? from what you describe, someone has bypassed the flame proving safety for that unit. If the HSI goes out, there is potential for that unit to dump gas because it always sees a flame. Not good.
    Was the original AC signal 115V?

  6. #6
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,653
    Wait a minute...what happens when the HSI is deenergized?

    Or I guess it never is?

  7. #7
    Join Date
    Apr 2001
    Location
    Western PA
    Posts
    1,801
    The flame sensor is wired to the neutral side of the ignitor, so it is always connected to the board's flame current circuit.
    There are not many of those old Rheems left in my area. They would have the most obvious and spectacular cracks, low in the heat exchanger. I like seeing one on a call!
    Jason

  8. #8
    Join Date
    Mar 2013
    Location
    Joplin,Missouri
    Posts
    310
    I just worked on one last week I'm glad there aren't many left I'm not a big rheem fan anyway

  9. #9
    Join Date
    Jul 2007
    Location
    Chicago IL
    Posts
    167
    HO says there hasn't been service work on the furnace in over four years when he replaced blower. Combustion was piped using the black PlexVent (80AFUE furnace) that I never see anymore. The flame rod wiring caught my eye as odd though I didn't have the Ok to start a diagnostic or at least figure how in the world it functioned. The piggyback onto the neutral was clearly not factory but I had no wiring diagram to check against. I was thinking maybe the board had been damaged and some clever tech managed to bandaid it. I'd never even heard of using the HSI to prove flame. The board didn't strike me as being a replacement either, I should have gotten the numbers off it in retrospect. After thinking about it, I can't ever remember seeing a Rheem with an HSI to begin with.

    I'm trying to get a print out of the original schematics from the local dealer to see what was there in the beginning. The unit is from 1992 in a house built in 1867. The furnace is hardly the only thing needing work in the system.

  10. #10
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,936
    Quote Originally Posted by fenian View Post
    I'm trying to get a print out of the original schematics from the local dealer to see what was there in the beginning. The unit is from 1992 in a house built in 1867. The furnace is hardly the only thing needing work in the system.
    I have the pre 1994 wiring diagram for this unit that shows this setup.

    If you can't get ahold of it, send me an email (address is in my profile), and I will get it off to you.
    Instead of learning the tricks of the trade, learn the trade.

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