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Flame Sensor, why Two Wires?

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I have an old Ruud Gas Furnace (model UGDA-12EA-GR ) from circa 1989-1990 that I suspect is in need of a new flame sensor due to the usual : fires up and immediately shuts itself down Symptom.

Contacted Ruud and they identified my model and provided me with the part number which is still in use today. I ordered the part and it’s on it’s way.

However, it’s clear the stock part has only one connection for one wire coming out of it. It’s part # 62-21744-01

But the current flame sensor (looks like a generic replacement) that is wired in but due to be replaced has two wires coming out of it. One connects to a red wire and one connects to a white/grey/yellowed wire. This seems inconsistent with the replacement part. Also most flame sensors seem to only have one wire as the flame is the positive and the wire is the ground completing the circuit.

Should I connect both wires to the same connection on the new sensor?

The only modification in my furnace i am aware of is that a glow fly igniter was put in place to replace the old igniter.


Thanks for your help.

Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    I'd recommend a qualified tech to check over the entire furnace for other possible dangers-like cracked heat exchanger and flame rollout. Then do a combustion test.

    There was an error rendering this rich post.

  • tacomancini
    tacomancini Member Posts: 5
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    Thanks Steve.

    I do believe it was serviced a few years ago, and he pumped it with foam to check for leaks and cracks. The flames ignited well and blue.

    To your point I am absolutely not qualified. Was hoping however I could do the flame sensor myself until I had the money to hire the pro. A new furnace is overdue.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    You sure your not mixing up the ignitor with the flame sensor. Sensor is just a metal rod with an insulator on the end with the wire coming off.

    I think the older Rheem/Rudd used hot surface ignitor. That glows red hot to light the gas off. They have two specially insulated wires and are very fragile and element cannot be touched with bare hands.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    On every Rheem I’ve worked in, looking at the burners, ignitor is on the right and flame sensor is all the way to the left.
  • tacomancini
    tacomancini Member Posts: 5
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    > @mikeg2015 said:
    > On every Rheem I’ve worked in, looking at the burners, ignitor is on the right and flame sensor is all the way to the left.

    I think my pic was. Upside down file some reason. It is in the left.

    Here’s another pic with the two white wires coming off of it.
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    IIRC, Rheem/Ruud of that vintage came out with HSI igniter and tried to have it do double duty as a FS..flame sensor.
    A few month in the field and the HSI got too cruded up to function as a FS. The company gave away the free FS add on kit just for asking, no paperwork.
    It mounted on the left side, had only one wire connected to the white (neutral wire....very important) with an insulation piercing tap. It had to be connected to the neutral/white wire only....the other black wire is 120 volt hot....you do not want the FS to be electrically "hot" in the furnace.

    It was another "put it out there and see if it works" field test that installers had to "fix" for them. I image every manufacturer does this to a certain extent.
    I bailed out of that brand name just as the "Drum heat exchanger" showed up. Never installed one.....I guess it was a big bullet to dodge. Now I hear fairly good things about the company.
    DZoro
  • ratio
    ratio Member Posts: 3,649
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    Does it glow orange-yellow when the furnace tries to light? It sure looks like a generic replacement igniter to me.

    The wires should end up on an ignition control board of some kind. Post a pic of that, showing the terminals, & someone should be able to identify it & tell you which wire goes to the flame sensor.

  • mikeg2015
    mikeg2015 Member Posts: 1,194
    edited November 2019
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    Your getting past my comfort zone. Looking at the style of burners (adjustable primary air). That might be a spark to pilot which is more like a boiler with 2 rods on some designs. Could be a combo sensor and ignitor that lights a pilot. But those usually have orange wires.

    I’ll look up that PN
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    > @JUGHNE said:
    > IIRC, Rheem/Ruud of that vintage came out with HSI igniter and tried to have it do double duty as a FS..flame sensor.
    > A few month in the field and the HSI got too cruded up to function as a FS. The company gave away the free FS add on kit just for asking, no paperwork.
    > It mounted on the left side, had only one wire connected to the white (neutral wire....very important) with an insulation piercing tap. It had to be connected to the neutral/white wire only....the other black wire is 120 volt hot....you do not want the FS to be electrically "hot" in the furnace.
    >
    > It was another "put it out there and see if it works" field test that installers had to "fix" for them. I image every manufacturer does this to a certain extent.
    > I bailed out of that brand name just as the "Drum heat exchanger" showed up. Never installed one.....I guess it was a big bullet to dodge. Now I hear fairly good things about the company.

    I think you are on to something.

    Every company has come up with solutions in search of a problem. Lennox Pulse, Carrier bristol compressors, Honeywell smart valves are awesome. :)
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    The part number you list is just a flame sensor. But it has a single spade terminal and one wire will go to it.

    If it’s 2 wires it a HSI.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    ... just to throw all this for a loop. Sometimes what looks like a bad flame sensor end up being a control board. It can be tested with a amp meter. Should give 1-10 micro amps. Usually these are so easy to remove we automatically clean them any time we touch a furnace to reduce risk of call backs.
  • tacomancini
    tacomancini Member Posts: 5
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    Thank you all so much for the help.

    I was indeed mixing up the igniter as the flame sensor. It does indeed glow. It is a Honeywell Glowfly igniter and according to the Glowfly manual it doesn’t do double duty as the flame sensor. This also goes along with the sensor part number that Ruud specified being a flame sensor only. I hope I didn’t damage it sanding it with emory cloth. Still does it’s glow thing though.

    I’m not sure where the flame sensor is.

    I shot a video of the startup sequence of the furnace glowing igniting and shutting off:

    https://youtu.be/X6TKLBqGqSU
  • ratio
    ratio Member Posts: 3,649
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    The grey box under the burner is the ignition control. I'm a little sketchy about the configuration, but ISTR that the little jumper on the right has to be clipped off to use a separate flame sense rod from the ignitor. Goggle the model number & you should be able to come up with an installation manual for it.

    It's time to start looking at the unit schematic too. Hopefully, it's still glued on the inside of one of the doors. If not, Google is your friend. It looks like several parts have been replaced with generics.

  • DZoro
    DZoro Member Posts: 1,048
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    Forget the flame sensor, you really need a new furnace.

    From the looks of the flame rollouts, your playing Russian roulette with that running in your home.
    Can't see from here but I'd be betting the H/E is cracked up.

    D
  • tacomancini
    tacomancini Member Posts: 5
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    > @DZoro said:
    > Forget the flame sensor, you really need a new furnace.
    >
    > From the looks of the flame rollouts, your playing Russian roulette with that running in your home.
    > Can't see from here but I'd be betting the H/E is cracked up.
    >
    > D


    Yikes. I hope not but it is surely at the end of its life.