The "EXTRA LOW" burners on the cooktop just stopped working. The igniters will not spark and I get no gas flow from the burners. If I light the regular burners to the right, the XLO ignitgers will spark. I opened up the unit and checked, there are no shorted out wires and everything "looks" normal. Can someone tell me if the problem is the valve, XLO feature, the igniter or what?