Kenmore oven not keeping temperature

My kenmore oven is not keeping the correct temperature. For reference, its model number is 75321 and it is fitted to run on LP gas. It is about 15 y ears old.
Upon looking into this, I found two likely scenarios:
1) bad bake igniter 2) bad temperature sensor.
Because there are two igniters, one for bake (below) and one for broil (abo ve), I figured that if the bake igniter was failing, I could simply swap th e two igniters - because it is highly unlikely that both would be bad (sinc e we hardly ever use the broiler). However, when I swapped the two, I see exactly the same problem. I also measured the resistance on both igniters and on the temp sensor.
The online troubleshooting videos tell me that the resistance of the temp s ensor should be between 1000 and 1100 ohms. Mine was around 1080. They al so tell me that the resistance for the igniter should be between 0 and 1100 ohms, but I think that is just a test for continuity, and doesn't tell me if it's failing or not. My two ignitors were around 180 and 190 ohms respe ctively.
Doing some trouble-shooting, here is what I see:
- When I turn the oven on, the igniter glows, but it takes about 5 minutes before the flame comes on, which seems too long, but maybe that's typical.
- Under normal operation, when the oven is on and has come up to temp the f lame goes off. When the oven has sensed that the temp has dropped too much , the igniter comes on again to relight the flame. Currently, the igniter comes on for about 35 seconds, after which the flame does *NOT* come on and the igniter goes off again. This cycle repeats every couple of minutes un til such time as actual oven temp has dropped enough that the difference in temperature between the oven and the set temp is pretty large (in the rang e of 100 to 150 degrees) at which point, the gas will come back on after ab out 35 seconds and eventually warm the oven back up to temperature.
- If I've set the oven for 350 and the flame has gone off, when the oven is trying to relight the flame, I can temporarily set the oven to 500 and the flame will come back on and stay on (even when I have returned the thermos tat to the desired set temp). But this hack is not that useful because und er proper operation, the flame will come on and off frequently to keep the oven temp within 25 degrees or so of the desired temp. So while this hack did allow me to bake cookies and cupcakes without ruining them for my daugh ter's birthday party recently, It's not convenient to stand by the oven for the entire baking duration (especially if cooking meat).
I think this sounds like the behavior of a failing igniter, the only reason I am skeptical is that both igniters seem to exhibit the exact same behavi or when installed in the bake position. Sadly, I didn't actually didn't te st their performance in the broil position.
It seems unlikely that both igniters would go bad, but I do have some dim r ecollection of this problem happening before - but no recollection of actua lly swapping the igniters. If I actually did swap the igniters previously and then failed to order and install a replacement for the one that went ba d, and the brain cells remembering that have died away, then I'm sorry for wasting your time.
If this sounds like the typical behavior of a failing igniter, then I will try and order a replacement and see if that works, but is there any other l ikely scenario that might be causing these symptoms? Could the problem be further upstream in the electrical chain in a place that is likely unfixabl e by a DIY enthusiast? Is it time to get a new oven?
I guess if it sounds like it could be the igniter, I will certainly try the $25 solution before proceeding to other more costly options - though it wo uld be good to know if there are other possibilities out there that I shoul d be looking at.
Thanks.
-J
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Sounds more like the gas valve is not turning on the gas. If the ignitor c omes on, buy no flame, that is no gas. Can you put a voltmeter on the conn ections to the gas valve and see if power is applied at the right time, and then see if the gas comes on when the power is applied to the gas valve.
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On 3/8/2016 3:04 PM, snipped-for-privacy@att.net wrote:

Could also be a thermal sensor (or, any of the associated mechanism) that determines the igniter is hot enough BEFORE turning on the gas (lest the house fill with unburned gas due to a failed igniter!)
I.e., is the igniter not getting hot enough? Or, is the thing that determines how hot it is not accurately sensing that?
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On Tuesday, March 8, 2016 at 6:21:02 PM UTC-5, Don Y wrote:

I've never seen a gas appliance where there is a sensor for the ignitor temp. Ignitor comes on, few secs later gas gets turned on, then there is a flame sensor to detect that it's successfully lit. That's how every one I've ever seen works.

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On Tuesday, March 8, 2016 at 5:05:07 PM UTC-5, snipped-for-privacy@att.net wrote:

nnections to the gas valve and see if power is applied at the right time, a nd then see if the gas comes on when the power is applied to the gas valve.
+1
Since it seems to fire when the temp diff is large, I'm wondering is it a dual stage valve and it works on high, but not on low, or intermittently on low? I'd put a meter on the gas valve, see if voltage shows up when the ignitor starts to glow. If it does and it doesn't light, could be the gas valve. Also seems odd that the ignitor would ever glow for 5 mins. I haven't worked on gas ovens, but similar, eg furnace, if flame isn't detected within maybe 20 secs or so of the gas valve going on, it shuts off, throws a fault code, etc.
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Well, I ordered an igniter. Will see if that fixes it. If not, I'll dig deeper and let you know. Thanks for the replies.
-J
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On Thursday, March 10, 2016 at 7:53:21 PM UTC-5, J wrote:

Interesting, since no one here said it could be the ignitor. Probably because you said the ignitor comes on, stays on for a long time, but it doesn't light. If the ignitor is glowing, how could it be the ignitor?
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On 3/11/2016 8:55 AM, trader_4 wrote:

The igniter on a stove has to draw a certan amperage for the gas valve to open. I've seen one where the ignitor glowed, but the oven did not light.
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On Friday, March 11, 2016 at 10:16:34 AM UTC-5, Stormin Mormon wrote:

Interesting, I wouldn't think it would work that way, but I have more experience with furnaces, WHs, etc.
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On 3/11/2016 11:37 AM, trader_4 wrote:

This I know, working on one gas range. I was thinking to replace the gas valve. Called the parts house. The counter man asked about the amp draw of the ignitor. And that turned out to be the problem. Ignitor had a small crack. Wrong amp draw.
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Are you saying that the amp-draw of the igniter is being monitored for the ignition logic ? ... or that perhaps the amp-draw is a symptom of a problem ... John T.
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On 3/11/2016 12:46 PM, snipped-for-privacy@ccanoemail.com wrote:

As it was explained to me, the amp draw needs to be at least # amps, and less than ## amps.
If the ignitor is broken or cracked, the amp draw may be too low. Symptom of cracks or breaks.
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OK,
I'm not sure of exactly how the electrical stuff works (even after asking m y wife the physics professor), but with the new igniter, the oven now seems to be working correctly. Yay!
Here is my limited (and possibly incorrect) understanding of how it is work ing:
From reading various posts online, it seems the igniter needs to draw a cer tain amount of amps for the gas to start flowing. I believe there is some kind of switch/valve/whatever controlling the gas, and that it will not ope n and allow the gas to flow unless a certain current is reached. I'm prett y sure this is a purely mechanical/electrical switch, not based on some log ic board measuring the current and deciding it's OK to open the gas valve. When the current reaches a certain threshold, it just opens. I'm pretty su re this is a safety feature to prevent your house from filling up with gas. I'm guessing that the current draw is a proxy for how hot that igniter is getting, thus the logic: "don't let the gas flow unless the igniter is ho t enough to actually ignite it".
I'm not exactly sure how these elements fail, but this is clearly not a "co mpletely dead" scenario. In any case, as I said, I had measured the resist ance of the two igniters at around 180 - 190 ohms (at room temperature). W ell, the new part had a resistance of 70 ohms. If you believe that V=IR, then the current (I) = V/R, and thus the old (failing) part would only d raw a little over 1/3 of the current as the new part under similar conditio ns. Now, I'm sure the resistance changes with temperature, and I'm not sur e exactly how the oven logic board operates, but clearly under certain circ umstances, even with the failing igniter was able to achieve enough current draw to allow the gas to flow - and those circumstances seemed to be when the differential between set temp and actual oven temp was large enough. T his likely had something to do with the logic board deciding for how long t o send current through the igniter.
So, there you have it. I think.
Thanks for everyone's input.
Now I'll order the replacement for the broiler igniter right away and repla ce that one so that this scenario doesn't play out again in another 10 year s :-)
-J
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On Friday, March 11, 2016 at 1:31:25 PM UTC-5, J wrote:

ms to be working correctly. Yay!

e kind of switch/valve/whatever controlling the gas, and that it will not o pen and allow the gas to flow unless a certain current is reached. I'm pre tty sure this is a purely mechanical/electrical switch, not based on some l ogic board measuring the current and deciding it's OK to open the gas valve . When the current reaches a certain threshold, it just opens. I'm pretty sure this is a safety feature to prevent your house from filling up with ga s. I'm guessing that the current draw is a proxy for how hot that igniter is getting, thus the logic: "don't let the gas flow unless the igniter is hot enough to actually ignite it".

stance of the two igniters at around 180 - 190 ohms (at room temperature). Well, the new part had a resistance of 70 ohms. If you believe that V=I R, then the current (I) = V/R, and thus the old (failing) part would only draw a little over 1/3 of the current as the new part under similar condit ions. Now, I'm sure the resistance changes with temperature, and I'm not s ure exactly how the oven logic board operates, but clearly under certain ci rcumstances, even with the failing igniter was able to achieve enough curre nt draw to allow the gas to flow - and those circumstances seemed to be whe n the differential between set temp and actual oven temp was large enough. This likely had something to do with the logic board deciding for how long to send current through the igniter.

ars :-)

Thanks for the update. Stormin had it right and looks like the rest of us learned some useful info.
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On 3/12/2016 8:01 AM, trader_4 wrote:

scenario doesn't play out again in another 10 years :-)

I'd like to thank my mother and father and my friends who made this all possible. And the man at the parts house who explained HSI and oven gas valves. And thank you Miss Strite, my second grade teacher, and.....
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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