Turn the gas off and allow the area around the gas log to vent for at least five minutes prior to doing any work. After five minutes, there should be no odor of gas. If the odor of gas continues after turning the gas switch to the off position open several windows in the house and call the gas company.
Use a flashlight to illuminate the area and find the pilot light. It is usually located at the base of the logs. Follow the gas line coming in and the pilot light will be at the end of the line. The control knob will be located at the front right or left of the base of the log unit. It is normally covered by a metal grate.
Place to control knob in the pilot position and observe the pilot light. It should be a pale blue color and slightly yellow at the top. The flame should encompass the thermocouple. The thermocouple is a small metal bulb located at the end of a copper tube.
Find the pilot light adjustment screw. It is usually located at the base of the pilot light where the gas line enters. Use a long handled, narrow tip, flathead screwdriver to turn the adjustment screw both in the clockwise and counterclockwise position. Turn the screw in the direction that will minimize the pilot flame. Then turn the screw back in the direction that expands the pilot flame so it fully encompasses the thermocouple.
Turn the control knob to the on position. Turn on the fireplace. Observe that the main log flame lights within a minute. Turn the control knob back to the off position and observe that the pilot light remains on. If the pilot light fails to remain on the thermocouple has air bubbles, is loose or has failed. Re-attempt to light the pilot light several times to make sure any air in the thermocouple has been removed.
Wait for the thermocouple to cool if the pilot light fails to remain on after removing the air bubbles. Turn the thermocouple clockwise to make sure it fits finger tight. A thermocouple fitted to loose or too tight may not work properly. If the thermocouple is finger tight and the pilot light will not stay lit, replace the thermocouple.