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Thread: Horizontal furnace flame sensor

  1. #1
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    Horizontal furnace flame sensor

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    Got an American Standard furnace in an attic. Previous tech had replaced the HSI a week ago. Today I cleared the clogged inducer hose and replaced a failed gas valve. I got the error of burners on with no call to gas valve. I noticed the ignitor on the bottom burner with the flame sensor on the same burner. The ignitor glowing right next to the flame sensor. I couldn’t find a install manual or anyone to ok moving to the top burner. My boss said NEVER move the FS from factory position. I wanted proof that it should be on top, or else it would not sense the flame on the burners.

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    Sounds like you walked into a real shit show! That's unbelievably dangerous for a manufacturer to put the flame sensor near the hsi. The whole reason it's always away from the hsi is to ensure that all burners actually light.

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  4. #3
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    Is it possible the tech mounted the hsi in the wrong spot? Could it have been mounted at the top? Then it would be opposite the flame sensor.

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    Last edited by JayMan7; 10-29-2020 at 10:13 PM.
    "I think Quantum tunneling would work great... "

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  5. #4
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    "I got the error of burners on with no call to gas valve"

    That's scary as hell! That right there is very problematic. Maybe you need to condemn the furnace to avoid liability until you have a chance to solve the issue. The flame sensor being close to the hsi wouldn't cause that issue. So it sounds like you have another electrical issue going on.

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  7. #5
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    Did moving the sensor clear the code?

    Id be surprised if so. Heat does not generate electron flow.


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  9. #6
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    Quote Originally Posted by heatingman View Post
    Did moving the sensor clear the code?

    Id be surprised if so. Heat does not generate electron flow.


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    That was my thought as well. It's the flame that's slightly conductive. Heat isn't going to affect the sensor. That's what's so disturbing. Even if the sensor is moved that's not going to resolve the more serious issue of a burner being on without a heat call

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    Quote Originally Posted by ksefan View Post
    I couldn’t find a install manual or anyone to ok moving to the top burner.
    There is nothing in the Installers Guide, or any other publication on this model that indicates the location of the Flame Sensor and Ignitor.

    The parts list kind of hints at the fact they are both on the first burner, because they are both pictured on the left side of the burner assembly picture, but it is not definitive.
    Instead of learning the tricks of the trade, learn the trade.

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  12. #8
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    I have several times come across horizontal mounted furnaces with the ignitor at the top of the rack and the flame sensor at the bottom. Usually removing and reversing the rack end-for-end solves the random lockout problem. Although I wouldn't hesitate to manually relocate them myself if that was required to make the lightoff consistent.



    Quote Originally Posted by ksefan View Post
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    Got an American Standard furnace in an attic. Previous tech had replaced the HSI a week ago. Today I cleared the clogged inducer hose and replaced a failed gas valve. I got the error of burners on with no call to gas valve. I noticed the ignitor on the bottom burner with the flame sensor on the same burner. The ignitor glowing right next to the flame sensor. I couldn’t find a install manual or anyone to ok moving to the top burner. My boss said NEVER move the FS from factory position. I wanted proof that it should be on top, or else it would not sense the flame on the burners.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

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  14. #9
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    Look at the picture of the burners. There’s a hole up top where the flame sensor should be mounted. Some hack has been messing around in this furnace


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  16. #10
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    Quote Originally Posted by JayMan7 View Post
    Sounds like you walked into a real shit show! That's unbelievably dangerous for a manufacturer to put the flame sensor near the hsi. The whole reason it's always away from the hsi is to ensure that all burners actually light.

    Sent from my SM-G960U using Tapatalk
    They never mount them on the same burner. Have you ever seen it ? I never have.
    Someone has modified this unit


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  18. #11
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    Quote Originally Posted by Bobe5531 View Post
    Look at the picture of the burners. There’s a hole up top where the flame sensor should be mounted. Some hack has been messing around in this furnace


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    I noticed that hole as well. I was wondering if either the fs got moved or the tech moved ths hsi when he installed it.

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    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  19. #12
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    Quote Originally Posted by Bobe5531 View Post
    They never mount them on the same burner. Have you ever seen it ? I never have.
    Someone has modified this unit


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    No I've never seen that before. It's unbelievably dangerous because what I have seen plenty of times is the hsi burner light without other burners lighting

    Sent from my SM-G960U using Tapatalk
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

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  21. #13
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    you know the class clown in school ?

    they get jobs .... and they like to move stuff around just to mess with the next guy

    Ive gotten parts out of the box assembled wrong

    it happens

    I would definitely move the flame sensor to the opposite side of ignitor where every manufacturer in the world places it ...

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  23. #14
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    I moved it to the top, everything worked fine.

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  25. #15
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    Quote Originally Posted by ksefan View Post
    I moved it to the top, everything worked fine.
    Great! I kinda line up with PHM. Part of the horizontal install instructions may have been to move it depending if it's laid left or right. Hence the other mounting hole.

  26. #16
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    On Trane Am Std on a furnace as oriented the HSI would normally be at the top and FS at the bottom. I have not done any upright to horizontal conversions to know if the HSI and FS are supposed to switch location as the HSI is mounted with 2 screws and the FS is mounted with the ceramic going through a hole with a screw holding it in place. In the picture such holes appear to have been stamped where the FS should be mounted.

    As to the flame sense with no call to the valve. The HSI is basically a small electric heater. As such there would be electron flow around the heater causing it to get hot. So the FS may have sensed the electron flow around the HSI rather than heat.

  27. #17
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    Oh man. I had a coworker do that on a new LP install because the burners wouldn't light. All I had to do to fix it was bump up the pressure at the regulator which he could have done if he'd known how to use a manometer. Sometimes what you find is terrifying and I'm not even that good of a tech but I'm good enough to know when I should be scared.

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  29. #18
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    Quote Originally Posted by BNME8EZ View Post
    On Trane Am Std on a furnace as oriented the HSI would normally be at the top and FS at the bottom. I have not done any upright to horizontal conversions to know if the HSI and FS are supposed to switch location as the HSI is mounted with 2 screws and the FS is mounted with the ceramic going through a hole with a screw holding it in place. In the picture such holes appear to have been stamped where the FS should be mounted.

    As to the flame sense with no call to the valve. The HSI is basically a small electric heater. As such there would be electron flow around the heater causing it to get hot. So the FS may have sensed the electron flow around the HSI rather than heat.
    Id have to test that theory. But I don’t believe that to be the case.

    Matter of fact, Trane RTU’s and some Lochinvar boilers have no flame sensor at all, they use the hot surface ignitor as the flame sensor.

    Some early HSI rheems did the same thing back in the 90’s. They had problems and came out with a kit that added a secondary flame sense rod that wired to one wire of the the HSI to increase the surface area for rectifying flame current. If I recall right, it tied to the hot wire leading to the HSI.

    Also, smart valve systems have the little HSI pilot with the sense wire right next to it. No flame no sense even with the ignitor glowing.


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  31. #19
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    Quote Originally Posted by heatingman View Post
    Id have to test that theory. But I don’t believe that to be the case.

    Matter of fact, Trane RTU’s and some Lochinvar boilers have no flame sensor at all, they use the hot surface ignitor as the flame sensor.

    Some early HSI rheems did the same thing back in the 90’s. They had problems and came out with a kit that added a secondary flame sense rod that wired to one wire of the the HSI to increase the surface area for rectifying flame current. If I recall right, it tied to the hot wire leading to the HSI.

    Also, smart valve systems have the little HSI pilot with the sense wire right next to it. No flame no sense even with the ignitor glowing.


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    As you say it is just a theory. I remember some of those with the HSI/sensor combo. Trane had some 2 burner furnaces for a while that were that way.

    Back to this situation, looking at the picture I was trying to tell which was the actual sensor. There is one to the right of the manifold with a pink connector on the end, that looks like what the sensor normally looks like and it that position. The other one, on the left of the manifold, looks like it only has 1 white wire on it also. That one almost looks more like a spark ignitor than HSI unless it is like a Glowfly but I still only see the one wire going to it. Maybe the OP can fill us in on that, as it is not a normal Trane ignitor that I have seen.

  32. #20
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    The previous tech replaced the carbide igniter with a nitride I believe.

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