Fireplaces, Heating Stoves, Flues and Chimneys - Gas Fireplace shutting off

I have a vented gas fireplace with an on/off (light-switch). Had the fireplace about 6 years. Worked great, then all the sudden when the fire was on, it went out on it's own (pilot light still lit). Sent for a repair man and first he replaced the switch. The fireplace worked again for about 3 days and went out again. Repair man came back and cleaned the unit and told me that "soot was built up", The fire place worked about a week then went out again. Since then I can get the fireplace to light and stay on for either a few moments or minutes or a day or two, then it won't switch on for another few days. Didn't call the repair man back yet, any ideas? How do I try to clean it myself, this seemed to work the best so far? Any help is appreciated! Calling for an ice storm tonight and the fireplace is my heat source if the electric goes out.

Mine are unvented so my experience is limited with the other type. I had a similar problem with an old set of logs. The burner would light then go off and sometime later come back on. Since your pilot stays on I suspect a similar problem.

Does your fireplace have a thermostat? Look for a metal bulb with a small tube attached near the front of the unit. The bulb will be located well away from the burner and pilot. If defective, this can cause the burner to go out before the room is warm.

If you discover a thermostat and the fireplace becomes your only source of heat, you might try placing a damp rag on the bulb. This may keep the burner on longer. Please do not go to sleep or leave the house with the rag in place. Gas appliances should never be cheated except in an emergency.