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  1. #1
    Join Date
    Aug 2007
    Location
    Billings, MT
    Posts
    81

    GCS3 ignition failure

    I'm servicing a Lennox GCS3-953-250a-7 (manufactured in 1972!) for ignition failure (CO readings tested by gas company a few months ago; unit is safe to run). The inducer comes on and closes the proving switch. The ignition control board energizes and the ignitor is sparking but the control board never sends voltage to energize the gas valve. My first thought was a bad board, but after swapping the board with a known good board (that functions just fine in the unit next to it) I can eliminate the board.

    This unit is located in a local convention center where inexperienced $9 an hour in-house maintenance has "repaired" it for the last forty years and with an unreadable schematic I'm at a loss as to how the controls are supposed to be wired. I could spend all day following each wire to reverse engineer a schematic, but I'm hoping somebody here will have access to a schematic. The reset commonly found behind the blower access panel has been bypassed and removed at some point.

    Also, any experience with this would certainly be appreciated. I only got about 45 minutes to look at it before a heavy rain started and forced me off the roof. I'm returning tomorrow and would appreciate any wisdom you may have picked up on these units over the years.

    Thanks!

  2. #2
    Join Date
    Jul 2007
    Location
    Virginia
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    5,858
    Quote Originally Posted by MontanaBighorn View Post
    I'm servicing a Lennox GCS3-953-250a-7 I could spend all day following each wire to reverse engineer a schematic, but I'm hoping somebody here will have access to a schematic.
    Check your email.
    Instead of learning the tricks of the trade, learn the trade.

  3. #3
    Join Date
    Aug 2007
    Location
    Billings, MT
    Posts
    81
    sir,
    i never took the time to thank you for taking the time to provide me with the necessary manuals. for this i apologize! thank you sincerely for providing the documentation; it made ALL the difference in the world.

  4. #4
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,858
    Quote Originally Posted by MontanaBighorn View Post
    sir,
    i never took the time to thank you for taking the time to provide me with the necessary manuals. for this i apologize! thank you sincerely for providing the documentation; it made ALL the difference in the world.
    I appreciate that, and glad it was of some help.
    Instead of learning the tricks of the trade, learn the trade.

  5. #5
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    19,321
    ....and what did you find....???????
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  6. #6
    Join Date
    Mar 2012
    Location
    Georgia
    Posts
    21
    Time for a new RTU!

  7. #7
    Join Date
    Feb 2011
    Location
    OH
    Posts
    149
    RUNDAWS IVE WORKED WITH SO MANY PEOPLE THEY SAY BETTER LUCK THAN SKILL .I LIKE ,INSTEAD OF LEARNING TRICKS OF THE TRADE LEARN THE TRADE SO TRUE ...

  8. #8
    Join Date
    Oct 2011
    Location
    Toronto
    Posts
    35
    Quote Originally Posted by MontanaBighorn View Post
    I'm servicing a Lennox GCS3-953-250a-7 (manufactured in 1972!) for ignition failure (CO readings tested by gas company a few months ago; unit is safe to run). The inducer comes on and closes the proving switch. The ignition control board energizes and the ignitor is sparking but the control board never sends voltage to energize the gas valve. My first thought was a bad board, but after swapping the board with a known good board (that functions just fine in the unit next to it) I can eliminate the board.

    This unit is located in a local convention center where inexperienced $9 an hour in-house maintenance has "repaired" it for the last forty years and with an unreadable schematic I'm at a loss as to how the controls are supposed to be wired. I could spend all day following each wire to reverse engineer a schematic, but I'm hoping somebody here will have access to a schematic. The reset commonly found behind the blower access panel has been bypassed and removed at some point.
    Also, any experience with this would certainly be appreciated. I only got about 45 minutes to look at it before a heavy rain started and forced me off the roof. I'm returning tomorrow and would appreciate any wisdom you may have picked up on these units over the years.

    Thanks!
    Are you referring to the limit switch?

  9. #9
    Join Date
    Aug 2012
    Location
    willowick ,oh
    Posts
    261
    i say gv open or shorted coil. soooooo. whats the verdict

  10. #10
    Join Date
    Oct 2009
    Location
    Ontario, Canada
    Posts
    831
    Quote Originally Posted by heresjohnnyb View Post
    i say gv open or shorted coil. soooooo. whats the verdict
    Well he did say that the board isnt sending a signal to the gas valve. But Im with you as there isnt much left at that stage of the startup sequence. Inducer has proved and it wouldnt try for ignition if a safety/rollout was open. Id put on a manometer and see if theres any pressure at the valve at all during the trial for ignition phase. I know with some of the older blue Johnson ignition modules that you need to have all the grounds installed just right to get it to work. Theres one on the valve body, and a common for the MV and PV (if so equipped).
    Get money, get paid.

  11. #11
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    19,321
    Quote Originally Posted by RayD8630 View Post
    Well he did say that the board isnt sending a signal to the gas valve. But Im with you as there isnt much left at that stage of the startup sequence. Inducer has proved and it wouldnt try for ignition if a safety/rollout was open. Id put on a manometer and see if theres any pressure at the valve at all during the trial for ignition phase. I know with some of the older blue Johnson ignition modules that you need to have all the grounds installed just right to get it to work. Theres one on the valve body, and a common for the MV and PV (if so equipped).
    Ah....what is he doing to find out why.....?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  12. #12
    Join Date
    Feb 2008
    Location
    Vancouver, BC
    Posts
    41
    Quote Originally Posted by MontanaBighorn View Post
    I'm servicing a Lennox GCS3-953-250a-7 (manufactured in 1972!) for ignition failure (CO readings tested by gas company a few months ago; unit is safe to run). The inducer comes on and closes the proving switch. The ignition control board energizes and the ignitor is sparking but the control board never sends voltage to energize the gas valve. My first thought was a bad board, but after swapping the board with a known good board (that functions just fine in the unit next to it) I can eliminate the board.

    This unit is located in a local convention center where inexperienced $9 an hour in-house maintenance has "repaired" it for the last forty years and with an unreadable schematic I'm at a loss as to how the controls are supposed to be wired. I could spend all day following each wire to reverse engineer a schematic, but I'm hoping somebody here will have access to a schematic. The reset commonly found behind the blower access panel has been bypassed and removed at some point.

    Also, any experience with this would certainly be appreciated. I only got about 45 minutes to look at it before a heavy rain started and forced me off the roof. I'm returning tomorrow and would appreciate any wisdom you may have picked up on these units over the years.

    Thanks!
    Just curious if you found out what was wrong or not. I'm having the same problem with a GCS3-413. There was a no heat call from the tentant, came up to the unit and found out that the fenwal ignition board was faulty, replaced it with a working board and now it doesn't send power to the gas valve. The 120v gas valve has been replaced with a 24v valve, there is a 120v-24v stepdown transformer, so the board closes the gas valve circut and sends 120v to the transformer which sends 24v to the valve, opening it up. I have spark but no bang.

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