I have a kenmore gas oven that will not light. When I turn on the oven the igniter heats up but the burner will not light. I have had it worked on before but it only seemed to help for a short while. The repair man replaced the clock, it did help but I have replaced the clock twice now and am having trouble again, is there anything else that could be causing this problem? I have removed the bottom cover in the oven, and cleaned the orifices on the burner they appeared to be clean, what else can I do?