Southbend GS Oven

[fordrules]

I'm working on a Southbend oven. Model: GS/15SC Serial:16E40781. This oven is stacked above an older southbend, flues tied together. The lower oven has no issues, and performs flawlessly. The ovens share a gas supply, and are on separate outlets.

The problem I have is the top oven will light, drop out the flame, and do this three times till it locks out on ignition failure. Originally, I cleaned the flame sensor and polished the burner by it. This originally had the fenwall ignition control, so I checked microamps at the board. It showed 3 microamps, but still locked out.

I ordered a board and replaced it. New board does the same thing. Now I dive a little deeper. I pulled apart and re connected all molex plugs. Confirmed incoming power is wired correctly, and transformer is wired correctly. Ignition board gets constant 27 volts through the ignition trials. Gas valve outlet is steady at 4" wc as per name plate. The blue Replacement board doesn't have pins to check flame sense, so I hooked my meter in series with the flame sensor. 0 micro amps when it lights.

Boss says order flame sensor. I order flame sensor, still same issue. I did measure ohms from where the flame sensor plugs in, to where the sense wire pin on the ignition board is, as it goes through a few other connectors, 0 ohms. I also ran a jumper wire from the burner frame to the ignition board ground, no change.

I did check the convection fan. It is running in the right direction, and stays on the whole time. Flues are still attached and seem fine. I really thought this was a flame sense issue.
But after really watching this, with a nanometer, and meter on the gas valve pins, it seems the flames light, swirl around, and almost snuff out. Then the control drops out. From what I see the wheel didn't have any plastic or big chunks in it, flues seem fine.

Any ideas? Most of the time I just change ignitors or motors on these. Thanks

[VanMan812]

Near the end of your post you say the “flames light, swirl around, and almost snuff out. Then the control drops out”

Sounds like the gas is dropping out before flame is proved and then the control drops out. You have 4” at the valve outlet though. I wonder if there’s a burner or orifice issue?

I had an Imperial do something like this a couple months ago. Several techs went out and replaced everything in the flame circuit only to still have the original flame rectification issue present. I noticed my microamps would start high but after a few seconds it would drop dramatically. The burner had a bunch of hairline cracks by the stamped out holes that caused the flame to waver and wander. New burner, no more issues.

Or I wonder if you have a hole in your combustion chamber somewhere and the convection blower is blowing air into the burner area.

Or a bad brand new module.


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[EjBreeze]

Make sure the plugins connector strips for the Fenwall module have a solid contact. I hate this Southbend model. This seems like a common problem with these. I'm not sure what you mean with the flame swirling around? I once had a tech install a new motor on a Southbend but placed the mounting plate back on the oven in a different position. Normally this wouldn't matter but it did with this Southbend oven.

[Turtleman]

You mentioned different outlets, have you verified you have a good ground on the troublesome unit.

[fordrules]

Found the problem after talking with tech support. There are two solenoid actuated damper plates that are used to save heat when the burner isn't running.

The linkage rods had broke off the damper plates. This caused an incorrect air/fuel mixture, as explained to me by tech support.

[VanMan812]

Well how about that! I can’t remember seeing a damper system in this model before, even on newer ones. I wonder if it’s an option.

Well I’m glad you solved the problem.


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[Chicharronne]

I have a double stack Southbend ovens with a common gas line. The bottom is a marathoner that is older with no more name plate data. The flame sensor was burn in 2, so it was an obvious problem. It's still failing, but not when I'm there. After reading the posts of failure after all ignition parts replaced, makes me hesitant to replace module.

[ECtofix]

I have a double stack Southbend ovens with a common gas line. The bottom is a marathoner that is older with no more name plate data. The flame sensor was burn in 2, so it was an obvious problem. It's still failing, but not when I'm there. After reading the posts of failure after all ignition parts replaced, makes me hesitant to replace module.

Been awhile since I've worked on a Southbend, but I remember they use an HSI for ignition and a rather longish flame-rod which does a 90° turn near its end to protrude over into the flame of far left in-shot burner.

Several things to look at before replacing the module:

• Make sure the flame rod tip is properly positioned in the burner flame so it easily glows red when the flame impinges on it.
• Make sure you have a good, clean BURNER ground back to the module (for the flame sensing circuit). Check both ground wire connections. Any corroded or iffy connections will serve as a resistance for the µA current the module needs to see to prove flame.
• It MIGHT be failing to light the burners due to an HSI that's on the verge of failure. It has a 24v HSI, so its resistance should test at around 4-5Ω. If it reads more than that, then it might have a hairline crack that's impeding its operation.
  In case you're wondering - YES, it CAN still glow, but could fail to get hot enough to light the burner.
• Make sure the burners are clean so that the flame spawned by the far right burner (the one the HSI ignites) will properly feed over to the center and left-hand burners.

Since you don't have a model #, this is the the first manual that popped up on the internet for a Marathoner:
https://www.middlebyadvantage.com/manuals/SLGS_spm.pdf