Gas cooktops are usually either sealed or twin burner models. Sealed burners have an igniter for each burner. All of the igniters operate on a single spark control. In a twin burner cooktop, which is found on some lift-top units, there are two igniters; one for the left side burners and one for the right. A malfunction in the switch mechanism or the igniter can cause your cooktop to click even if the unit is turned off. Clicking can also indicate that the unit is dirty or that the igniter or switch has been in contact with moisture.
Burner Not Shut Off
When you turn on a gas cooktop, the burners click as they try to ignite. It is normal to hear several burners click even if you're only attempting to ignite one. If your range clicks continuously when not in use, check the burners to ensure that they are all in the OFF position. On some units you have to make sure that the knob has popped back out to confirm it is off. If the igniters continue clicking long after they've ignited, or when the knobs are all in the OFF position, unplug your range, turn off the gas supply to the unit and contact a technician for service. The ignition system may be malfunctioning.
Cleaning the burners can cause intermittent clicking until the unit is dry. If moisture gets into the switches or the ignition area, they may not function properly. If you've just cleaned your cooktop, allow several hours for the igniters and the burners to dry or use a hair dryer on its lowest setting to speed up the process. If the noise continues after this time, contact a technician to inspect the unit.
Switch or Ignition System Malfunction
If the switch that controls the spark module has malfunctioned, you may hear clicking from the burners as they try to ignite when the knob isn't turned on. The igniter may also click if it is malfunctioning. You can test the switch and the igniter with an OHM meter. You can usually access switches through an access panel on your stove. Igniters are attached to the burners either from above or below. The switch can also become twisted and eventually break, causing the spark module to remain on, clicking even when the burner is already lit. If everything else is functioning, it may be that the spark module is malfunctioning and needs to be replaced.
Dirt or Grease
If the clicking noise occurs only after you light the burners, the electrode, which is the small metal piece on the burner that the spark comes off of, may be dirty or the holes in your burners may be clogged. Use a metal pin or a paper clip to clear the burner holes, and not a toothpick, which can break off. If the igniter or the electrode becomes caked with grease, the spark won't jump to the burner and your stove will not light. On most gas cooktops, you can remove the top part of the burner to clean this area. On sealed units however, you may need to replace the entire burner because you can't lift these off to clean.