I have a Thermador dual-fuel range, model PRD304WHU. One of the XLO burners is behaving oddly. When turned on, it lights and operates normally. However, after switching off, after 10-15 seconds the igniter starts clicking again as if it is trying to relight, even though the knob is switched off. I can get it to stop if I cock the knob slightly to the side, so that it is not in the fully off position but also not open to where gas would flow. It is only one burner that does this, the other XLO burner (and the regular burners) work normally. Any suggestions?