Gas fireplaces don't need a lot of maintenance, but you should inspect your unit before each burning season. See if there's been any change to the shape or color of the flames. A properly adjusted gas fireplace should produce blue flames with yellowish tips. (If your flames don't match, find the control panel and adjust the primary air shutter... if that doesn't fix the problem, you'll need to consult a specialist.)
Also check to see if soot has formed on the logs or windows. If this is the case, you should check with your gas supplier to find out if the composition of the gas has changed.
How to clean your gas fireplace:
- First, turn off the gas and electrical power and let your fireplace cool down.
- Remove the logs/stones/coals and the burner. Take them outside and with a soft-bristle nylow brush, clean them off. Similarly, scrub out the firebox and vacuum the dust.
- Turn off the pilot light and use a dry cloth to clean the pilot nozzle plus the burner asseembly. Before reassembling everything, turn on the pilot light to make sure it's burning properly.
- While you have your unit open, inspect the vents and make sure they are clean and clear.
- Use a non-ammonia-based household cleaner to clean the viewing glass.
- Lastly, replace the logs/stones/coals and burner to their exact location. Turn the power and gas back on and flick on your fireplace. Make sure the fire burns well and that you don't smell gas.
Source: Home Improvement 101