A thermocouple is a temperature-controlled switch built as a safety feature into many heat-producing appliances, including gas and electric fireplaces. At a preset heat level, the switch opens to disconnect power from an electric fireplace or shut off the valve in a gas appliance. If you have problems getting your fireplace to ignite or stay lighted, the thermocouple may be malfunctioning. A quick way to test the thermocouple is to bypass the part. This should only be done to diagnose problems, not as a permanent solution to a malfunctioning fireplace.
Shut off the fireplace using the control on your particular model. Wait for the fireplace to cool completely before running a bypass.
Remove the cover panel from the ignition system for your particular fireplace model. On some models, the cover plate snaps off with gentle pressure. Other models secure the cover plate with screws that must be removed with a screwdriver.
Pull the two wires off the thermocouple contacts using needle nose pliers to slide off the connector at the end of each wire. The thermocouple is mounted on a metal plate attached by screws to the burner assembly near the bottom.
Hold the two metal connectors on the wire ends together and tape loosely with a piece of electrician's tape.
Start the fireplace normally. If the appliance ignites, it means the thermocouple is bad and must be replaced. Shut off the fireplace and do not operate until the repair is complete.
Remove the two screws that secure the thermocouple to the burner assembly. Take the thermocouple to a repair shop to match with a replacement or order the part from the manufacturer of your fireplace.