Standing pilot (millivolt) models will require the pilot to be replaced every 5 years or so. If it's only been 2-3 years since replacing the pilot, you could try cleaning the pilot assembly with some very fine grit (300 grit and above) sandpaper or with an emery cloth to see if this corrects the issue, but contacting a local technician to check for other issues may also be a good idea as all gas fireplaces should be cleaned and maintained annually. We recommend using the National Fireplace Institute Website to locate a gas specialist in your area.