Turn off the Thermador controls. When the stove cools, close the gas valve behind the appliance, turning the lever on the valve clockwise.
Unplug the Thermador's power cord, which provides electricity to heat the ignitor.
Remove the service panel on the back of the Thermador using a screwdriver. The ignitor assembly consists of a flat prong resembling a thin, metal fork connected to a ceramic or resin block. A pair of wires from the block are permanently attached to a plug that fits in the power socket inside the Thermador.
Disconnect the wired plug from the back of the defective part.
Twist the two screws holding the part counterclockwise to remove the ignitor from the bracket that holds it in front of the gas valve.
Set the new part in the same position and tighten the two screws securely. Do not touch any part of the metal tip.
Connect the wired plug to the power socket.
Reconnect the service panel with screws to the back of the Thermador.
Open the gas valve.