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Flame rod shorted ground?

FBOVE
FBOVE Member Posts: 5
in Gas Heating
80% 25 year old gas furnace. WR 50A55-112 module. Problem - After many years no problem, problem started, inducer on, fire up 3to4 seconds flame goes out inducer keep running, repeat 3 or 4 retries than lockout. Checked grounds, clean flame rod(remote) no better. Indicator light - no ignition. Replaced module. Problem changed, inducer on,flame on 3to4 seconds than flame and reducer off. Repeat 3 or 4 times than lock out. 6 flashes on module which was not listed on menu, only went to 5. search of web found 6 flashes - flame sensor problem possible short to ground. I checked what I knew how to, could not come up with short to ground. Replaced sensor, problem seems to be resolved.
What are checks for finding a flame sensor shorted to ground?

Comments

  • ChrisJ
    ChrisJ Member Posts: 16,316
    edited March 2016
    Check with an ohm meter between the sensor wire and ground?

    I have no idea, but that would be my first step as I assume the flame rod to ground should be open when disconnected from the module.

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

  • FBOVE
    FBOVE Member Posts: 5
    That was checked. No continuity to ground. Even heated sensor thinking heat would open a crack or simulate operating conditions. And again new sensor seemed to solve problem.
  • ChrisJ
    ChrisJ Member Posts: 16,316
    @captainco may be able to give some input on this.

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

  • ChrisJ
    ChrisJ Member Posts: 16,316
    edited March 2016
    @FBOVE Only guess I have at this point is perhaps your ohm meter isn't good enough for this task.

    Perhaps a megohmeter would've shown different results.

    The rod may have not had sufficient insulation from ground at 24V but was perfectly fine at 1.5 - 9V.

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

  • JUGHNE
    JUGHNE Member Posts: 11,276
    FBOVE, did your testing have the same clamping device on the sensor insulator as the actual installation would of had.

    If the insulating material had almost invisible cracks and moisture had entered then the resistance to ground would have dropped. Heating it up would actually drive out the moisture (if there) and perhaps improved the resistance.

    As ChrisJ said a Megohmeter would show the true resistance, but is an expensive tool for a homeowner versus the few dollars for a new FS.
    If I was doing the TS and got that code I would change FS and if it fixed it I would be done. (but still wonder about the part failure....maybe take it home hoping to test it sometime).
    Call backs cost time and credibility to the service person.
  • FBOVE
    FBOVE Member Posts: 5
    Tested sensor installed in furnace room temp and out of furnace. I do get the point, high resistance maybe. There is a long story with this. 4 service calls to get to point issue resolved.
    Trying to figure out if I could have used different procedures, to eliminate call back and credibility issues. Do not own a megger.
    Really wondering if shorted to ground had a different meaning than I understood it to be.
    Thank You for replies
  • JUGHNE
    JUGHNE Member Posts: 11,276
    Are you homeowner or serviceman?
  • FBOVE
    FBOVE Member Posts: 5
    Service
  • JUGHNE
    JUGHNE Member Posts: 11,276
    I am familiar with the repeat service calls that are non-profit and instill the creditability issue in HO.

    Other than a good meter or Megohmeter I have no idea of testing FS it looks good physically. Maybe someone here has had that experience and can explain.

    With the new module it seems the inducer fan should have kept running for post purge though??
  • BobC
    BobC Member Posts: 5,502
    I've used megohmmeters for most of my life and the old style were pretty dear. I did a brief search and turned up this one that might be a good option for a reasonable price, looks like it applies 500 to 2,500v for testing..

    http://www.ebay.com/itm/1-x-BM3549-Megohmmeter-Digital-Insulation-Resistance-Tester-Multimeter-FREESHIP-/251958240293?hash=item3aa9e1a425:g:cS8AAOSwPhdVUwI2

    You might check with your supply house to see if they have something similar.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Tim McElwain
    Tim McElwain Member Posts: 4,642
    I have a step by step procedure for testing for these units being shorted along with other technical difficulties. It is contained my Electric Ignition Systems Volume I manual sold here on Heating Help. However if you contact me I will make a copy of just that section for testing you are looking for. Call me at 401-437-0557 or e-mail me at gastc@cox.net I will send it off to you free of charge.
    SWEIRobert O'Connor_12
  • FBOVE
    FBOVE Member Posts: 5
    I will order the manual. I appreciate your offer Tim but we all have to make a living including you. Thank You
    SWEITinman
  • Tim McElwain
    Tim McElwain Member Posts: 4,642
    I look forward to hearing from you.

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