i have a Thermador Dual fuel range, the left front burner will not spark or emit gas the burner is a xlo. the right front burner will only spark and light off if the right rear burner is operating. I have checked all the connections to the Pot 1 and Pot 2 along with swapping out the leads and ignitors. Gas line to the left front burner is not clogged. The left rear which is also a xlo works fine. Range is approximately 12 years old and has been very reliable so far. Thanks