I service all gas fireplaces and log sets including vented, vent free, direct vent, and b vent. If your fireplace won't start when you turn it on, emits a strong odor, or shuts off shortly after you turn it on, you should have it serviced.
Problems can range from clogged burner, clogged pilot, bad wiring, bad thermo assembly, improper log placement (installation).
VENT FREE FIREPLACES are a special concern, because if they're not cleaned regularly, they will emit EXCESSIVE CARBON MONOXIDE.
Vent free fireplaces should be serviced yearly. Service normally takes about an hour unless parts are required.