oven temp sensor not working properly (I think)


We have a ~9 yr old Kenmore gas oven/range (runs on propane actually), and the oven temperature sensor appears to be flakey (the actual temperature in the oven is definitely flakey). The oven has a knob to set the oven temperature, and a digital display that shows the temperature you set, but it does not display the measured oven temperature - it only has a light that indicates if the oven is "preheated" (at the set temperature).
The oven heats up to the desired temperature just fine (as measured by an oven thermometer) and the "preheated" light comes on, but at some point, the temp inside the oven will drastically decrease, with no external signs of trouble. The "preheated" light remains on and no error code is displayed. With an oven thermometer in the oven I can confirm that the oven does get up to the set temperature as expected, but if left on for a while, it will at some point cool down way below the set temperature. For example, I set it to 375. It warms up just fine. I start baking something. I check on it 1/2 hr. later and the temp is down at 250! The oven seems to think everything is OK though; the "preheated" light is still on and there is no error code displayed - I'm not even sure if this model has error codes to display. At this point, if I turn the oven temp knob to off and then back to my desired temperature, it will then notice that the oven is too cool and warm it up again.
I can order a replacement temperature sensor and install it, but before I shell out the $75 + S&H (which seems like a lot), I'd like to know that the problem is most likely the sensor and not some obvious other problem.
So, does this behavior sound like a faulty temperature sensor?
Thanks.
-Jonathan
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It sounds like an electronic component which is faulty. The temperature sensor inside the oven sounds like it is detecting the temperature, but there would probably be some other electronic chip or circuit which should "recheck" the temperature, then turn the oven back on.
You would need to look at a wiring diagram for the oven to see how it works.
"JJ" wrote in message

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If your oven ignites with a glow bar rather than a pilot, it could be the glow bar is defective. The glow bar is responsible for opening up the gas valve after it reaches a certain resistance. But if defective, the resistance changes and thus the gas valve is not opening when it should.
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Ugh! I was afraid it might be a little more complicated. I don't seem to have a wiring diagram. The oven does use a glow-bar. I wish I could isolate the problem.
I'm hesitant to call a repairman - especially since the problem seems intermittent and can take a half our or more to present itself (if it does at all). It may end up costing as much as the oven did originally. My wife called a repairman for our dryer a little while back. He replaced a $20 belt in about 5 minutes, that I could have easily replaced myself. Total charge was over $200.
If anyone else has tips on what I might do to figure this out, I'd really appreciate it. I'm pretty confident about replacing parts, though I'd be likely to call in a professional if the repair looked like it might get too intimate with the actual gas-flow.
Thanks.
-Jonathan
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Unfortunately there's no way to tell if you have a defective glow bar in this situation. They go for about $25 on e-bay. I've bought them before. If your oven has a broiler on top that uses a seperate glow bar, you could swap it to the bottom oven if its the same kind.
Usually when glow bars go dead, its easy to troubleshoot, just ohm out with a meter and if its open, it's no good. But this is different since it's intermittent.
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JJ wrote:

Try www.repairclinic.com. They have some diagnostic stuff that may help.
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If you want to repair things yourself, you need the right tools. That being a wiring diagram and a multimeter.
You can get service manuals and wiring diagrams from the manufacturer. Maybe from their web site. With some appliances, wiring diagrams are pasted inside one of the covers for the appliance.
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Check Sears web site. See if you can locate a diagram to help dianose problem. WW
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I found the wiring diagram (in a pocket on the back of the oven) - but it's a bit beyond my ken. However, last night I spent some time looking for behavior patterns. What I found was that once the oven reached temperature, the glowbar and burner would go off as expected. Some time after that, (presumably when the oven needed warming to stay at temperature) one of 3 things would happen: 1: I the glowbar would start to glow, then after a short time stop glowing - no gas. 2: the glowbar would glow, then the gas burner would come on and then go off again almost immediately. 3: The glowbar would glow then the gas burner would come on and stay on for a while, heating up the oven (proper functioning).
So it seems likely that the problem is with the glow bar (or possibly some logic chip) - but it seems to be intermittent. I'll test it with an ohm meter, but that my be inconclusive. It looks like the glow bar for the broiler is the same part, so I'll see if I can swap them for now and see if that fixes the oven problem. I tested the broiler and it seemed to be functioning properly (#3 above).
Thanks for your inputs.
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As a follow-up, I thought I'd post and let you know that I was able to swap the top (broil) and bottom (bake) glow-bars, and this did resolve oven temperature problem. Thanks everyone for their input.
I tested the broil function briefly (for about 15 minutes) and did not see any problems there either. I was kind of hoping that broiling would now not be working properly, as that would undisputedly finger the faulty part. Since this problem was intermittent, It could just be that I didn't test long enough to see the problem. Or possibly there was a flakey connection that was fixed during the swap. Either way, I now have a functioning oven. I almost never use the broil feature anyway, usually opting for the gas grill outside instead - so it may be a long time before I notice if the broiler is now malfunctioning.
-J
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