My oven will work if I use a low temp (200 to 250) or if I use a higher temp (400 to 450) but if I set it for 300 or 350 it might work once but then usually won't heat up right after that. I was wondering if the thermostat might be messing up? I hate to buy one if it's not that.

To clarify the problem better when I turn the oven on to 350 to bake the ignitor glows and when it warms up to tempature the burner will ignite and the oven will heat up. It reaches tempature and kicks off just fine the first time. When it cools down and needs to ignite and warm up again usually it will not warm up to the right tempature. If I use a cooler tempature or a hotter tempature to cook it works just fine.