Page 1 of 3 123 LastLast
Results 1 to 13 of 32

Hybrid View

  1. #1
    Join Date
    Jun 2005
    Location
    Colorado
    Posts
    34

    Flame sensor questions??

    I have 2 questions about flame sensors in residential furnaces maybe some out there can help me with. While doing a tune & clean on a furnace this week I hooked my meter in series with the sensor lead to check the micro amp output as I always do but when I disconnected my meter, and therefore the lead to the sensor was not connected, the burners stayed on. I let it run a few minutes, turned it off and on several times and each time the burners remained on. Normally the burners go out right away. I told the customer this was a potentially dangerous problem and the only solution would be to replace the control board. Any other ideas on this? My 2nd question is about the sensor output on some of the newer furnaces. When measuring the output the reading jumps around like crazy, anywhere from 0 to 8.0 or more. Any ideas on this one? Thanks for any input.[/SIZE]

  2. #2
    Join Date
    May 2004
    Location
    Salt Lake City/Tooele
    Posts
    2,431
    Flame sensor uA vary so much depending on the module, control, or board. In your case, if I had a basic furnace that was not shutting off on flame sense, I would assume the same. I agree that as rare as this is, that I would deem it as very unsafe, also.

  3. #3
    Join Date
    Dec 2010
    Location
    Virginia
    Posts
    353
    ran into samething yesterday that through me off right in front of the customer. I make a call for heat and the HSI lights the burners for about 2 to 3 seconds then the gas valve drops out. So presume the flame sensor is dirty, but wanted to check its output, so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp readingon my meter fluctuated from I believe it was .1 to .2, but the thing that was wierd to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out. I cleaned the flame sensor up real good, only because my company doesnt have any stocked on my truck or I would have replaced it, and works fine now. That is the way I was taught to check them, and didnt know exactly what my reading was suppossed to be but it seemed low and I was pretty sure the flame sensor was the issue.

  4. #4
    Join Date
    Dec 2007
    Posts
    4,670
    Quote Originally Posted by millertime77 View Post
    ran into same thing yesterday that through me off right in front of the customer. I make a call for heat and the HSI lights the burners for about 2 to 3 seconds then the gas valve drops out. So presume the flame sensor is dirty, but wanted to check its output, so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp reading on my meter fluctuated from I believe it was .1 to .2, but the thing that was weird to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out. I cleaned the flame sensor up real good, only because my company doesn't have any stocked on my truck or I would have replaced it, and works fine now. That is the way I was taught to check them, and didn't know exactly what my reading was supposed to be but it seemed low and I was pretty sure the flame sensor was the issue.
    what was your reading AFTER you cleaned it?

    .1 or .2 does seem low. usually want at least 1.0 if not greater.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  5. #5
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,356
    Quote Originally Posted by millertime77 View Post
    so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp readingon my meter fluctuated from I believe it was .1 to .2, but the thing that was wierd to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out.
    I just worked on a Carrier rooftop unit with this exact issue. It had an aftermarket board in it.


    with everything connected normal it would not sense flame and shut down. As soon as I put my meter in series with the flame sensor, everything ran fine and I got a 5 microamp signal. I hooked back up without the meter and it would no longer sense flame. WTF?

    I pulled the board from a neighboring unit and it worked fine in this unit. When I put the questionable board in the other unit it no longer worked at all. There must have been something wrong with the board so I am exchanging it. (only 5 months old, but has never run in heat mode)

  6. #6
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,800
    Quote Originally Posted by craig1 View Post
    I just worked on a Carrier rooftop unit with this exact issue. It had an aftermarket board in it.


    with everything connected normal it would not sense flame and shut down. As soon as I put my meter in series with the flame sensor, everything ran fine and I got a 5 microamp signal. I hooked back up without the meter and it would no longer sense flame. WTF?

    I pulled the board from a neighboring unit and it worked fine in this unit. When I put the questionable board in the other unit it no longer worked at all. There must have been something wrong with the board so I am exchanging it. (only 5 months old, but has never run in heat mode)
    Should have just left your meter in the circuit and charged the customer for a new meter.
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
    Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii

  7. #7
    Join Date
    Dec 2010
    Location
    Virginia
    Posts
    353
    Quote Originally Posted by doc havoc View Post
    Should have just left your meter in the circuit and charged the customer for a new meter.
    Why? Is that not how you are suppossed to check a flame sensor? Will it ruin the meter like that?

  8. #8
    Join Date
    Jan 2007
    Location
    DFW Texas
    Posts
    42
    Quote Originally Posted by millertime77 View Post
    ran into samething yesterday that through me off right in front of the customer. I make a call for heat and the HSI lights the burners for about 2 to 3 seconds then the gas valve drops out. So presume the flame sensor is dirty, but wanted to check its output, so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp readingon my meter fluctuated from I believe it was .1 to .2, but the thing that was wierd to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out. I cleaned the flame sensor up real good, only because my company doesnt have any stocked on my truck or I would have replaced it, and works fine now. That is the way I was taught to check them, and didnt know exactly what my reading was suppossed to be but it seemed low and I was pretty sure the flame sensor was the issue.
    I had a similar experience with a Ruud unit. On the 80 percent units you might try reversing the polarity. This has worked for me twice now.

  9. #9
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,475
    What kind of furnace? Some actually sense flame through the carbide ignitor.

  10. #10
    Join Date
    Jun 2005
    Location
    Colorado
    Posts
    34
    It was a 10 year old rheem. Pretty standard, HSI on the right, 6 in-shot burners and sensor on the left.

  11. #11
    Join Date
    Dec 2010
    Location
    Virginia
    Posts
    353
    It was over 1, if I remember correctly 1.2.

  12. #12
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,790
    i have this problem with rooftops i work on.

    heres another test for ya.

    let furnace run and unhook the flame sensor spade terminal and see if it runs.

    sometimes when i hook my meter up to it and take 1 lead off it still runs. if i put everything back to normal and pull terminal off board it cuts off.

    i notice on honeywell s8910u and johnson controls(blue box) they run in between .1 - 1

    a lot of others run from 3-6

  13. #13
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by gravity View Post
    i have this problem with rooftops i work on.

    heres another test for ya.

    let furnace run and unhook the flame sensor spade terminal and see if it runs.

    sometimes when i hook my meter up to it and take 1 lead off it still runs. if i put everything back to normal and pull terminal off board it cuts off.

    i notice on honeywell s8910u and johnson controls(blue box) they run in between .1 - 1

    a lot of others run from 3-6
    Its been awhile on this end, but does not the positive go through the carbon in the flame to the negative (Ground) and that amperage is what is measured?

    How does leaving a meter in the circuit, even partially, accomplish this task when the sensing end is disconnected?

    I realize a meter draws amperage as well, but dag gone that sure is some pretty scary flame rectification on this end.

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event