What could be wrong with gas fireplace that turns off when I turn it on?

Question

Pilot light is lit. When I turn it on, it starts up, normal amounts of flame. Then it turns a blue flame, and slowly disappears until even the pilot light goes out.

This was working not even 2 weeks ago, and to my knowledge, nothing has changed other than the temperature outside has dropped about 20 degrees.

Answer 1

My first guess would be the thermocouple is bad, or going bad. The thermocouple is a small device that generates electricity from heat, they are used in gas furnaces and such to shut off the gas in case the pilot goes out (so gas doesn't continue to flow and fill the room).

I admit I'm no expert when it comes to gas fire places, but I had an old gas heater that displayed similar issues and it turned out replacing the thermocouple fixed the problem. Besides they are usually fairly cheap (a couple dollars maybe), so it's a good place to start trouble shooting.

Answer 2

After reading @GalacticCowboy's answer it got me thinking, and after a little research I was able to find this.

Natural Gas contains a small amount of moisture (approximately < 5%) and this moisture will freeze in the winter in long exposed piping runs. Some of this moisture ends up in the gas pressure regulator and will freeze the diaphragm inside the pressure regulator causing it to malfunction or close off the gas feed.

Source

Not sure how cold it is where the problem is being experienced, but it is possible for the gas to be restricted by a frozen line.

This might also explain why it works temporarily. The line may not be completely blocked allowing gas to build up in the line beyond the blockage, when the fire place is turned on it burns up the gas in the line and then is starved once the initial build up is depleted.

This could also be caused by some other type of blockage, partially closed valve, improperly installed pipe, or some other type of blockage.

Answer 3

I think Tester101 is probably correct - at least it's a good place to start.

If a gas appliance will not light or stay lit, it is almost certainly one of two issues:

1. Too little oxygen - make sure any vents, flues, etc. are open and can breathe
2. Too little gas - either there is not enough pressure, the source is empty (in the case of bottled gas) or the flow is being reduced or cut off.

Most natural gases will have a blueish color to the flame. However, the color also tells you a lot about the combustion process. From what you're describing, it sounds like the flame is fuel-starved. Since you have a pilot light, you will definitely have a thermocouple as well - since the pilot runs on a very low flow of gas, the thermocouple is supposed to prevent the gas from flooding the room if the pilot goes out. As he described, a bad thermocouple will turn off the flow of gas even if it's not supposed to, resulting in fuel starvation.