Model # JGS8850ADS
, this all gas range had a cook top with burners that worked as expected, and the oven seemed to work OK using the broil mode. But when bake was selected, it seemed like it would work about 50% of the time. The customer noted that it could take nearly an hour to heat a pizza and even then it may not be fully cooked. The customer didn't notice any gas smell associated with the failure or any other thing out of the ordinary. But they did want it working properly again.
Gas ovens will generally use one of two methods to ignite gas for cooking. The first is a spark ignitor which functions much like the surface ingnitors in that the gas valve is turned on followed by a high voltage spark to cause ignition. The second is a glow bar ignitor that will begin to glow and generates heat when voltage is applied. As the temperature of the glow bar increases, the current draw will also increase, and the resistance in the wire will decrease. Once the resistance is low enough, the gas valve will open and ignition will occur.
The bake and broil burners on this range both used the glow bar ignition which helps explain the reason for this seemingly inconsistent failure. See as the glow bars age, their internal resistance will decrease resulting in lower temperatures when voltage is applied. For safety purposes, we want the glow bar to be well above the ignition temperature of the gas, so the valve is designed to only open when the ignitor achieves the correct temperature. The ignitor will glow bright red when we look at it, but the only way to verify it is operating correctly is to do a current check. This can be easily done by gaining access to one of the wires leading to the ignitor and using a clamp type amp meter.
The suggested minimum current draw for these ignitors was 3.2 - 3.6 amps and since I was reading less than 3 amps, I knew the ignitor needed to be changed. With the power removed I installed a new glow ignitor by removing the two mounting screws and one wire connector. With everything back in place, I tested the operation by starting a cooking cycle. After about 30 seconds the gas valve came on and the oven heated like it was new.
Just a note - these ignitors will begin to fail and the symptom will often be it will ignite the first few times and then it stops. Not a real big deal if you are cooking something quick, but a real hassle when making that lasagna. They will get progressively worse with time so if you notice your oven having difficulty igniting repeatedly, replace that ignitor before it fails when you really need it.
Jenn-Air Gas Oven Igintor Part # 74007498