GP51MP-24B-045-1 Hot Surface Ignitor replacement

Discussion in 'HVAC Heating & Cooling' started by Onkar Sharma, Nov 4, 2017.

  1. Onkar Sharma

    Onkar Sharma Member

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    Massachusetts
    Hi Stuff,
    Sorry. Just saw this. Will do this tonight and will post the results.
    Thanks.
     
  2. Onkar Sharma

    Onkar Sharma Member

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    Nov 4, 2017
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    Ok. So I did not know what you wanted me to measure. The leads feeding into the ignitor and ground, or the ignitor leads and ground. I measure both.

    1. Feed terminal 1- 0
    2. Feed terminal 2-0
    3. Ignitor lead 1- Cannot measure, just shows 1. I think it means infinity.
    4. Ignitor lead 2- Cannot measure, just shows 1. I think it means infinity.

    If you provide idea as to which one you were referring to, I can go to the basement tomorrow morning and remeasure for certainty. I am home tomorrow.

    The control board most likely will be here only on Monday.
     
  3. Stuff

    Stuff Well-Known Member

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    Location:
    Pennsylvania
    That was to verify a remote chance that the ignitor wasn't leaking to ground. It appears OK.
    For the feeds from the board: one should be zero but one should be a bit higher.
     
  4. Onkar Sharma

    Onkar Sharma Member

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    The board is almost here. If it comes today, I will install it and will let you know. Let's go from there.
     
  5. Stuff

    Stuff Well-Known Member

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    Good luck. Take a few more pictures for yourself to help to verify wiring connections afterwards.
     
  6. Onkar Sharma

    Onkar Sharma Member

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    Will Do. I am going to label each wire and pair it with the new board in my mind before I take it all apart.

    Should be easy. At some point I am going to retry prying the burner cover off. I think it is just stuck.
     
  7. Onkar Sharma

    Onkar Sharma Member

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    Thanks for all of your help so far. I am not out of the woods, but this is amazing progress for me.
     
  8. Onkar Sharma

    Onkar Sharma Member

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    Yay!!
    It looks like it is working. I will keep an eye on it for now, but all seems good. Thank you Stuff for all the kind help. I have a mass save inspection due in January (I will try to have it preponed). They should be able to give me an advanced thermostat for cheap.
    I will tackle lock change and a non-functional electric oven now.

    Will reach out once I am ready for thermostat change.

    Thanks once again
     
  9. Onkar Sharma

    Onkar Sharma Member

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    Not Fixed. It ran for a few hours. Now it is in watchguard mode. Alternate slow flashes. More advise needed.
     
  10. Onkar Sharma

    Onkar Sharma Member

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    The HVAC is now consistently in watchguard. I went to the basement to watch it go into watchguard. The flame lights for a second or two and then quickly dies. This goes on for 5 times and then the equipment goes into watchguard.
    From what I could read online, one possibility is that the flame sensor is dirty?
     
  11. Onkar Sharma

    Onkar Sharma Member

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    Nov 4, 2017
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    Update so far:
    1. Used scotch brite to clean the flame sensor. It was a little dirty. Problem persists.
    2. Placed the fan to on and then turned the furnace on. Still went into watchguard.
    3. Once just before watchguard came on, for a second or so, I saw green light on and the red light blink.

    Does this mean that the limit switch is also gone?
     
  12. Stuff

    Stuff Well-Known Member

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    Location:
    Pennsylvania
    Check the wire connection.
    From https://www.emerson.com/documents/commercial-residential/1547324.pdf

    Alternate slow flash
    External lockout
    (retries)
    Failure to sense flame is often caused by carbon deposits on
    the flame sensor, a disconnected or shorted flame sensor
    lead or a poorly grounded furnace. Carbon deposits can be
    cleaned with emery cloth. Verify sensor is not contacting the
    burner and is located in a good position to sense flame.
    Ignitor must be positioned to light the gas immediately when
    the valve opens. If the ignitor has been replaced, verify hot
    spot position has not changed.
    Check sensor lead for shorting and verify furnace is
    grounded properly.​
     
  13. Onkar Sharma

    Onkar Sharma Member

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    Thanks Stuff. I already cleaned the flame sensor. From the window it looked like it is in the path of flame.
     
  14. Onkar Sharma

    Onkar Sharma Member

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    I don't know if the flame sensor is bad. Please advise.
     
  15. Onkar Sharma

    Onkar Sharma Member

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    Just check the wire connection. It is going from Flame Sensor to The F.S. connection on control board. I already cleaned the flame sensor.
     
  16. Stuff

    Stuff Well-Known Member

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    Flame sensor is just a metal rod with an insulated base. Measure between the flame sensor wire lead feeding it and ground - should be infinity. Measure between wire and rod - should be zero across all of it. (clean it with steel wool, not chemicals which can coat it) Measure between the burner nozzle and ground - should be zero. Sometimes the FS is bent or out of alignment so make sure that you see it in the flame path.
     
  17. Onkar Sharma

    Onkar Sharma Member

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    Thanks Stuff. This all checks out. The rod looks straight and is in path of the flame.
     
  18. Onkar Sharma

    Onkar Sharma Member

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    Thank you Stuff for all your help.
    While we are diagnosing, I have a question. Are you suspecting the flame sensor? How about the high limit switch. These are cheap parts. Although it is not my preferred path, should I order both of them (just because it takes time for these to come)? I am worried that our Thanksgiving weekend will be spent in cold.
     
  19. Onkar Sharma

    Onkar Sharma Member

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    So I had a thought and measured again. The resistance between FS lead and ground is infinity. The Vac is 20. But I could not measure current. The Aac was zero. What does this mean? If this is not meaningful, let me know I can redo this quickly.

    The flame sensor is in pretty inaccessible place. I can take it out again to measure resistance across the rod but it will take time.

    From the look of it, the flame sensor is in front of the flame. The flame shoots across it.

    I do not have access to burners yet. I will try to tug out the burner cover once I am back from the swimming class.

    As I mentioned the flame sensor rod was cleaned by scotch Brite. No chemical was used.
     
  20. Onkar Sharma

    Onkar Sharma Member

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    Nov 4, 2017
    Location:
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    Hi Stuff,
    I just measure the resistance across the Hi Temperature limit switch. It was 1.5 ohms. Does it mean that the switch is bad?

    Let me know what you think?

    Thanks once again for the help and putting up with my questions and lack of skills.
     
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