GCS3 ignition failure

[MontanaBighorn]

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!

[rundawg]

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.

[MontanaBighorn]

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.

[rundawg]

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.

[timebuilder]

....and what did you find....???????

[Cold shot]

Time for a new RTU!

[david chamberla]

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 ...

[GastecD]

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?

[heresjohnnyb]

i say gv open or shorted coil. soooooo. whats the verdict

[RayD8630]

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).

[timebuilder]

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.....?

[Rossco]

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.