If the pilot light has gone out for an unknown reason, it helps to know how to test a gas fireplace thermocouple. The thermocouple prevents gas leaks by detecting the heat of the pilot light, but it eventually wears out.
Step 1 – Locate Gas Valve and Pilot Assembly
The thermocouple will resemble a long copper wire running between the pilot light and the gas supply valve. The pilot light usually looks like a narrow bent tube cut at a shear angle. Shut off the furnace gas to remove and clean the thermocouple if it is covered with soot.
Step 2 – Hold Pilot Open to Heat Thermocouple
Push in the control valve and light the pilot flame. Hold the valve open for several minutes; if the flame stays on when you release it then the thermocouple works. Otherwise, it may need to be replaced.
Step 3 – Watch Pilot with Main Burners On
Even if the pilot lights, a draft may have diverted it from the thermocouple. The thermocouple should sit in the top third of the blue cone of fire. Watch the flame during operation to see if it strays.