AI have a Bosch gas cook top (Model NGM3654UC/01) with a broken igniter. I can find the part but am at a loss as to how to remove the burner to replace the igniter. There is only a large nut on the top of the burner once you remove the burner caps but it only protrudes about 1/16 from the burner and I have not been able to turn it to loosen it. Any suggestions would be greatly appreciated.