Measure the millivolts on your Heatilator fireplace by using a voltmeter. Read the Heatilator owner's manual to determine the proper measurement process for your heater, because each model requires a different setting.
Look at the voltmeter reading to determine whether the millivolts are less than the millivolts recommended for your particular fireplace.
Adjust the pilot screw by turning it slightly counterclockwise with your fingers or a pair of pliers. This adjustment screw is generally labeled with the word "Pilot."
Test the amount of millivolts again with the voltmeter after adjusting the screw. Repeat the process if the millivolts reading is still not high enough.