Safety first
If you smell gas, do not try to light anything. Leave the house and call your gas utility from outside. Everything below assumes there is no gas smell.
The most common causes
A worn thermocouple or thermopile. These sit in the pilot flame and tell the gas valve it is safe to stay open. When they weaken, the pilot lights and then goes out, or the burner shuts off after a few minutes. This is the most common cause.
A dirty pilot. Dust, spider webs and soot can make the pilot flame weak or lazy, so it does not heat the sensor properly.
Dead batteries. Many remotes and receivers run on batteries. A weak receiver battery can make the fireplace act like it is broken.
A failing gas valve or control module. Less common, but when the valve or module fails the fireplace will not respond no matter what you do.
What you can check yourself
Replace the batteries in the remote and the receiver. Make sure the wall switch is on and the gas shutoff valve near the fireplace is open. Follow the lighting instructions on the label inside the unit. If the pilot still will not stay lit, stop there. The rest involves gas parts and should be done by a pro.
What the repair costs
Most repairs come down to one part. A pilot assembly usually runs $500 to $800, a control module $500 to $700, and a gas valve $900 to $1,300. We test the parts first and tell you which one it is before we replace anything. More on our gas fireplace repair page.