Lighting a Gas Fireplace in the Fall

I've had my gas fireplace about 8 years. At the end of the heating season, I always turn off the gas at the main tank. In the fall when I'm ready to light the fireplace for the first time, I turn the main gas valve back on. I've found that the button under the fireplace that needs to be pushed in when pressing the starting button has to be held in for a few minutes before trying to light the fireplace. This is because any gas left in the line between the propane tank and the fireplace evaporates over the summer. Hold the button in for a few minutes, then let it go. This gets gas back flowing from the tank to the fireplace. Once you've done this, light the fireplace with the starter button as usual.