Oven Ignition When Hot

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Old 11-28-07, 09:27 AM
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Oven Ignition When Hot

We have a older Kenmore gas oven that lights with a glow igniter. The igniter was replaced less than a year ago. The burner lights quickly and smoothly whenever the oven is cool, but does not relight once the oven is hot (as required to maintain temperature). The igniter heats up, the gas comes on, but the burner simply doesn't light, even after a minute or two. I noticed that it would sometimes light if I opened the broiler door for a few seconds. I cleaned the burner (a lot of dirt came out) and pushed a wire through the burner holes closest to the igniter. Still no luck. Any help would be appreciated.
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  #2  
Old 11-28-07, 10:20 AM
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Hello MedRest and Welcome to the Do It Yourself Web Site and to the Gas Appliances topic.

Hummm???...thinking of some possible causes...

You cleaned the burner slots/ports. Good start... Existing igniter not that old. Ok.

A Few Possible Causes: (If applicable)

If the cross over port/slot is also cleaned, burner should light on both sides. If burner only lights on one side, cross over slot/port clogged or expands too much when hot.

If burner does not light on both sides, cleaning cross over slot/port holes is required.

If cross over is a slot in an aluminum burner, which expands too much when hot (often fails to light on both sides of the burner) burner should be replaced.

If the burner fails to light totally, not good. Delayed ignition results. Delayed ignition is an explosion, when all the gas ignites at once. Serious and possibly dangerous condition.

Other possible but rare causes can be air to fuel ratio. Fuel ratio can vary with air temps. Try closing air shutter slightly. The air shutter is located on the base of the burner tube. Close air shutter only slightly. Not enough to cause yellow burner flames or yellow tipped burner flames.

In some cases the burners flame size needs to be adjusted lower. Lower (smaller) flames create less force which keeps gas nearer the igniter.

Flames must not exceed out-wards more then 2/3 rds of the flame spreaders size. Flame spreader is the plate attached to the top of the burner.

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Old 11-28-07, 12:09 PM
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Thank you for the ideas. Here's some more info that may help narrow this down.

The burner fails to light totally - I know - definately scary especially when I'm sitting there listening to the gas pour in for a little while.

I'm pretty sure the burner is steel - not aluminum. It is about 0.75" thick, 3 to 4" wide, and 10 to 12" long with a rounded end. Holes are spaced around the perimeter about every 0.25" (going from memory). I do wonder if it has something to do with burner expansion - I took it out to clean it while the oven was still quite warm and when I put it back in, it lighted perfectly. However, wouldn't relight again after being on a few minutes.

Adjusted the air flow from full open to full close to no avail.

Before replacing burner, I would like to try adjusting flame size, but don't know how/where. I assume if I can find the gas valve, I will find a regulator nearby? Also, don't exactly understand what the flame spreader is. The plate on top of the burner extends maybe 0.125 to 0.25" past the gas hole openings. When lit, the flame extends well past the top plate by another 0.125 to 0.25".

As before, thank you for providing a great service. Your insight is appreciated!
 
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Old 11-28-07, 05:27 PM
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Hello: MedRest

The flame spreader plate will be a steel plate that is usually attached to the top of the burner usually using a wing nut or wrench hex nut.

The flame spreader plate is about 2/3 thirds the width of the oven compartment. The plate is not all flat. It has a shape to it. Made of steel.

Based upon your description of the burner, 3-4 inches wide, I suspect burner is cast iron or chrome plated steel and flat. Not round as an aluminum tube would be.

Knowing the updated info you provided tosses out much of the previous possible causes, except for the air to fuel ratio and or flame size. Possible there may be other causes.

There should not be an aluminum foil in the oven anywhere. Baking compartment empty except for the baking racks.

Lets work with flame size since air shutter adjustment did not work. Be sure air shutter has been returned to it's original position or at least 2/3 rd's or more opened. No yellow flames must be present. All blue and not lifting away from burner nor blowing.

To adjust flame size, only if the flames exceed the width of the flame spreader or more then 2/3 rd's it's width.

The orifice will be located just below the air shutter. A brass or bronze hex head nut. The burners gas inlet sits on the orifice hex nut. Adjusting the orifice clock wise reduces the flame size. Counter clock wise increases flame size.

Be aware that not all orifices are adjustable. Sum are pre-set and do not adjust. This can apply to any gas orifice.
 
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Old 11-29-07, 11:46 AM
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I believe the orifice is fixed - definately doesn't turn easily. Repeated whole exercise today. Burner lights within seconds when cold. Leave it burn for even just 1 minute - turn off oven - turn on oven - and burner won't light. Hold a match adjacent to the glowing ignitor and the burner lights perfectly. I found that I have to hold the match about 0.25" to 0.5" closer to the burner than the ignitor.

Is the ignitor too far from the burner? I installed the new ignitor a year ago, and I'm sure it is similar to the old one, and within 0.125" of the location of the old one.

Is the burner flame too low? It only projects about 0.5" from burner hole and the ignitor coil is about 1.5" away. How do I adjust the flame if the orifice is unadjustable?
 
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Old 11-29-07, 11:51 AM
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Whoops - a few more details
The oven is a Kenmore model 911-3128612.

The burner is sheet metal - porcelain coated. Shaped somwhat like an oblong pancake.

The flame is perfectly blue no matter what I do with the air shutter. Only difference is how loud the gas noise sounds. I adjusted the shutter to about 1/2 open.
 
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Old 11-30-07, 10:25 AM
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Is the ignitor bracket expanding somehow when the oven is hot and moving the ignitor farther away? Can you check the model #? I can't get it to work at Sears parts website.
 
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Old 11-30-07, 11:08 AM
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Hello: MedRest

Clues are likely in next to last post. Excerpts quoted below to highlight and emphasize.

Hold a match adjacent to the glowing ignitor and the burner lights perfectly. I found that I have to hold the match about 0.25" to 0.5" closer to the burner than the ignitor. Is the burner flame too low? It only projects about 0.5" from burner hole and the ignitor coil is about 1.5" away.
If the burner flame is as small as you mentioned and not reaching out toward and near the end of the flame spreader plate, I suspect the gas valve is not opening fully after it's initial opening. Cold start versus warm starts.

As mentioned before, the burner flame must not exceed 2/3 thirds the width of the flame spreader plate. Nor should it be less the 1/2 the width of the spreader plate.

If the flame size looks sized correctly, as described above upon initial cold fire up and then is as drastically reduced upon warn fire ups as you noted in your post, then I suspect the gas control valve is defective.

The point here is to notice flame sizes. Flame size would be an indicator of a defective gas valve. Flame size should be the same size each time the burner lights. (2/3 thirds the width of the flame spreader plate and not less then 1/2 the width of the spreader plate)
 
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Old 12-02-07, 08:56 AM
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Flame size is the same when it's cold and hot.

Ignitor is not moving in any noticeable way when it changes from hot to cold.

My theory now is that the gas flow/pressure is too low, so once the burner is hot, the updraft pulls the gas up and away before it reaches the ignitor. The direction I'm getting here regarding flame size versus spreader plate do not seem to make sense with this burner construction (described earlier).

I just need to know if there is a way to adjust the gas flow/pressure.

I will double check the model number and repost ASAP.
 
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Old 12-02-07, 09:08 AM
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Hello: MedRest

There is no gas pressure adjustment on the gas valve. If you suspect the gas pressure is to low, and cannot adjust the orifice to change the flame size, replace the gas valve.

Once that is done, post back the final results.

"Be sure the electrical power and the gas supply to the appliance is turned off, before attempting any repairs. Always check for gas leaks whenever the appliance is moved and/or a repair includes any connection of a gas part."
 
  #11  
Old 12-03-07, 08:12 AM
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Corrected model number on this unit is 9113128812
 
  #12  
Old 12-03-07, 12:03 PM
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Fixed!!! It was flame size - no new parts required. The orifice was adjustable after all, just much tighter to turn than I expected. Thank you for all of your assistance and for saving me the cost of a service call!
 
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