What a service visit covers. We clean the logs and embers and set them back where the manufacturer intended — logs in the wrong place put the flames on the logs, and that is what makes soot. We clean the burner and the pilot assembly, clean the glass on sealed units, and then light the fireplace and watch it run: the pilot should hold, the burner should light smoothly, and nothing should be sooting up.
The vent side. We check the parts that carry exhaust out of the house. For gas logs in a brick fireplace, that is the flue, the cap and the damper. Decorative gas logs vent up the old chimney, so the damper must not be able to close; the fuel gas code (IRC Section G2453) requires a permanent opening for unlisted log sets, which is why you will often see a clamp holding it open. For factory-built gas fireplaces, we check the vent, the termination cap and the chase cover.
Vent-free logs have no flue to inspect. They need to be kept clean and run according to the manufacturer's instructions, and the CPSC says never to operate unvented fuel-burning appliances in any room where people are sleeping.
Where we draw the line. We service the fireplace. We do not install or alter gas piping: in North Carolina, running a new gas line or changing the existing one is licensed fuel piping work (G.S. 87-21). If the problem turns out to be in the gas supply, we will tell you, and a licensed fuel piping contractor or your gas utility takes it from there.
If you ever smell gas in the house, leave first and call your gas utility from outside. Don't book a service visit for that. For more on whether a gas fireplace needs sweeping, see does a gas fireplace need a chimney sweep?