Check for soot
The beginning of a soot buildup problem may not be noticed by the naked eye. To check for soot, turn off the heat and allow the log to cool. Take a clean white cloth and wipe down the ceramic gas range and fireplace door (if you have one) in your fireplace. If you see thick black marks on the cloth, you have a soot problem. Another sign of soot is the accumulation of small clumps of a black, powdery, gray-like substance on ceramic logs and glass fireplace doors.
Cause of accumulation
The most common causes of soot buildup in gas fireplaces are ceramic matches being moved out of place and clogged burner ports. If the logs are displaced, they can interfere with the flame path that ensures the gas burns cleanly, causing soot to form on the logs and door. Another major cause of soot is clogged ports on gas burners, which can cause incomplete or uneven combustion and build up soot on logs and doors. In either case, clean the firewood and door, and make sure the firewood is in the exact location specified by the gas burner manufacturer. If the port on the burner is clogged, follow the manufacturer's instructions for cleaning it or have it cleaned by your fireplace dealer.
Air flow
The correct fuel-air mixture in a fireplace produces a nice yellow flame with minimal soot buildup. Front-loading gas fireplaces usually have a damper on the gas line feeding the burner to regulate the fuel-air mixture. On fireplace models with glass doors, an adjustable ventilation louver under the door adjusts the amount of combustion air. Dampers or vents must be clean, unobstructed, and in place. If the flame is starved of air, excess soot can be produced.
Ageing
Gas fireplace burner sets eventually wear out or rust, causing them to emit gases in different ways and volumes than when they were new. This different flame pattern can lead to "dirty" combustion and soot buildup. The match itself may have cracked or broken off, striking the flame path and interfering with normal combustion. Another possible problem is a clogged fireplace vent or chimney. If you don't find any problems with your gas fireplace but still experience excessive soot buildup, have your gas supplier check that the gas regulator supplying your home or fireplace is adjusted and functioning properly.
