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Flame Sensor Wire Not Connected ... is it dangerous?

edward1977 Member Posts: 1
I have a 1990 vintage Rheem gas furnace with HSI , HS780 controller and "Standard Blower Control" board. The furnace stopped working, but, after some fiddling, decided to start up again today. The problem was that gas would not turn on after the HSI started glowing.

It is working now, but I noticed that the flame sensor wire is not connected ... it is just ends with a wire nut that someone put on the end.

Is the system OK with the flame sensor hooked up? Also, I have examined the schematic on the door of the furnace repeatedly, and I cannot find any "Flame Sensor" component. Is it possible that the function is done via the HSI hookup, or in some other indirect way? If so, it seems odd that there is a standard rod-type flame sensor installed in the unit.

Thanks for whatever you can tell me!


  • SlamDunk
    SlamDunk Member Posts: 1,487
    If what you are describing is accurate, yes. It is dangerous. If the safety relay has been compromised to think there is a flame when there isn't, you could dump raw gas into unit all night long if there is nothing to ignite it.
    JUGHNE Member Posts: 10,792
    That vintage of Rheem originially came out with the HSI doing double duty of lighting and flame sensor.
    Apparantly it became obvious that the HSI would not always prove flame (this may have happened to you just now).
    So an add on factory kit for flame sensor was furnished. It mounted on the opposite side of the burnner rack. The wire of it was tied into the white side of the HSI???....don't recall...can't look...not home now. An add on wiring diagram and notice sticker was included. A line tap connection was also included. May be that the install was never completed. With burner on full and if you unplug the HSI aka flame sensor, the gas should shut off. If not, then you have a serious situation and should shut the furnace completely off.
    JUGHNE Member Posts: 10,792
    Note: do not attempt to connect FS to HSI unless you sure of which side of HSI to use. I'm on the road and can't look it up. Tim would probably know off the top of his head........(my head is getting older now and don't want to say with out papers in front of me)
  • Tinman
    Tinman Member Posts: 2,806
    edited January 2016
    JUGHNE is correct. Rheem, at first, used local sense through the ignitor on the HS780 control. There were issues so they added a Remote Flame Sensor Kit. The number on the kit was #AS-58494-01. That number may be helpful to the technician you call.
    Steve Minnich
    JUGHNE Member Posts: 10,792
    You should look for the instruction sheet for that AS-58494-01.
    It is 6 pages long and applies to 3 different Rheem furnaces. The connection is to the neutral/white wire on the connector side before the HSI plug. You must check the voltage to ground on the white wire with HSI disconnected but the power on trying to light the furnace (with the gas service valve shut off for this testing). The HSI operates with 120 VAC while warming up, so you don't want the new flame sensor to have the hot 120 to ground.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    Stephen beat me to it. Make sure you have a pro check it so you can follow the directions which should be downloaded or contact Rheem for copies. I looked all over here in the office and can't find my instructions for AS-58494-01. We have had similar changeouts from White Rodgers Cycle Pilot by Weil- McLain going to HSI on HE and VHE boilers quite a few years back.

    Maybe one of you that has that instruction could e-mail me a copy at [email protected] just in case I can't find mine. Someday when I retire I will have time to put some order to this office.
  • Tinman
    Tinman Member Posts: 2,806
    Tim - I will scan and email you a copy in the morning.
    Steve Minnich
  • minhdo64
    minhdo64 Member Posts: 2
    My flame sensor wire open ( not connected ). Can you send wiring diagram where flame sensor wire connected?
    JUGHNE Member Posts: 10,792
    You are tailgating onto a 5 year old posting.
    For your system a lot more info is needed.

    Furnace....boiler.....water heater....RTU...????

    Pictures of components and what does it do or not do?
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,126
    @minhdo64 please start a new post so your discussion doesn't get lost at the bottom of this old one. Thanks!