I have a Gaggenau 2 burner gas cooktop--Model # VG 223-812, Serial # 8711--ignites by turning either of the knobs, depending on the burner, and pressing down on the knob. When the knob is depressed and held, there is a spark which ignites the gas burner. Now when I turn the knob and press down, there is no spark generated--I have to light by hand. Can I purchase a replacement part and how difficult is it to repair/replace the part? Do I need a manual for this? Thank you. Marty Kline 301.651.3453