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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.

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Have you had any problems with other gas appliances? Is the temperature below freezing when you notice the problem? –  Tester101 Nov 22 '10 at 17:27
    
Ghosts. But Tester101 makes a good case, too. –  msanford Dec 6 '11 at 20:05
    
This sounds like a bad regulator.. if allows enough gas to pass to fill the line to supply the pilot and to start the fireplace, but quickly runs out and everything halts. –  HerrBag Feb 25 '13 at 20:34
    
Model and age of fireplace would help. Various brands have their own common problems. –  Bryce Dec 24 '13 at 20:03
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4 Answers 4

up vote 8 down vote accepted

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.

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This sounds to be the deal. As of today, the pilot light even fails to light. I have the gas company coming out tomorrow. –  esac Nov 23 '10 at 1:24
    
You need the fireplace vendor out, not the gas company. The gas company likely won't replace your thermocouple. –  Bryce Dec 24 '13 at 20:04
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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.

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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.

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Wouldn't the flame go out immediately though if the thermocouple were incorrectly shutting off the gas? –  Mike Powell Nov 22 '10 at 14:28
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@Mike Powell: It should go off quickly, but could be slowed by a "sticky" valve. The OP does not say how long the whole process takes (from normal flame to not flame), so it could be a couple hours or a couple seconds. –  Tester101 Nov 22 '10 at 17:24
    
It is a couple of seconds. –  esac Nov 23 '10 at 17:44
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I have the same problem with my gas fireplace. Whenever the temperate drops below 20 degrees outside, the pilot goes out. So far it has turned out that a water pipe in the street freezes and breaks, water gets into the gas line and weakens the gas. The first time it happened I thought something was wrong with my fireplace. Then I found out later that my neighbor on the corner of my block furnace went out. They spent $800 on a furnace repair man trying to figure out what was wrong with their furnace. After about a week, all of a sudden our whole street was torn up because a water pipe was discovered broken and getting into the gas line. This year it happened again. My pilot light went out and sure enough a water pipe was broke down the street about 5 days later.

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I don't believe this is a case of correlation equaling causation. –  BMitch Dec 25 '13 at 12:26
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