My oven has been taking a long time to heat up. Now it will not start. Broiler ignites fine. Oven ignitor is brilliant Bright Orange, & has no smell of gas. Tried to light with a Flame to see if igniter was not hot enough to allow ignition, with NO luck.
Reviewed parts listing and not sure if my trouble shooting diagnosis is correct! Valve, gas AP3970480 needs replacement, in that the valve solenoid is not opening to let gas out.
Most likely the problem with your oven is a bad igniter.
You can learn how the oven igniter works from the one of my previous posts here: http://forum.appliancepartspros.com/oven-repair-including-ranges-cooktops/1897-oven-wont-lite.html
The bracket for the igniter you can use from the old one.
Gene.
[COLOR=#333333]THANK YOU GENE! How Can I say it! Saving me $$$$ & Time. Your response and answer was 110% correct. I have recommended [COLOR=#800080]AppliancePartsPros.com[/COLOR] to more people than I can count in this last week since I fixed my oven. Dollars saved on the part from a retail service company, not to mention the 4 hours of waiting at the house to meet the technician to fix the application, as well as the service charge for coming to the house. I replaced the igniter & fixed the oven in less than 15 minutes and I’m a hero 
with my wife!
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