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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.

  • 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
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    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
  • @tester101 I am having the issue you described. What do you think it may be? – bigmike7801 Dec 31 '17 at 18:21

11 Answers 11

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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
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    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.

  • It's the gas valve, +1. OP: "As of today, the pilot light even fails to light." – Mazura Jan 23 '16 at 23:18
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I don't think it is a thermocouple problem, or water in the gas line as I have seen this here in California which sounds similar. The fireplace turns on with a nice flame and then goes to blue and then woof, it and the pilot flame are extinguished. This only occurs in the minutes after start-up and does not occur when the fireplace has been running for more then ten minutes. Cause: At turn-on, there is significant oxygen and the fire consumes the oxygen, but there is a problem, the consumed gas needs to push the heavy and dense cold air in the chimney up out of the pipe in order to draw fresh oxygenated air down the biconical pipe to feed the fire. During that critical time, if the exhaust gas is not able to push through the cold air in the exhaust stack, no new air is drawn in and the fire quickly runs out of oxygen and the flame and pilot light are snuffed out. This gets worse on cool days. To solve, make sure the exhaust stack and intake pipes are clear. If that doesn't work, you can try this, you won't like it, but it works for me: you watch the flame at start-up and turn it off before it turns blue and extinguishes itself, then wait two minutes, try again, but be sure and turn it off before it goes completely blue. On the third attempt, there should be enough latent heat to force a channel of air up through the dense cold air and then your fire should continue burning. I plan to look at side venting to avoid the cold exhaust stack problem.

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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.

  • 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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exact same problem... i used a straw and blew out the little holes on top of the thermocouple and also around the pilot light... before i could get the pilot to light but i had to hold the button down for almost a minute for it to stay lit then 30 seconds after turning it on everything would go out... since i blew it out unblocking any blockage its been lit for 2 days now

  • I was having the same problem. I took a straw (as suggested) and blew out any dust that may have been in the pilot light, and around the thermalcouple. I now have a strong bike, torch like flame coming from the pilot light. Seems to be working now. I hope it lasts! Thank you for the straw idea! – Laurie Dec 4 '16 at 13:22
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I had the exact same problem with my propane fireplace. After investigating some of the suggestions above I realized that it was a gas supply problem. Knowing that my tank was full I was worried that there was a blockage in the line. But I soon realized that the problem was simply caused by the valve on the top of my propane tank not being opened enough. When my tank was filled last the delivery man had not turned the valve enough. There was enough gas to run the pilot light but not enough sustain a flame for more then a few seconds. Opening the valve solved the problem.

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    This makes a lot of sense. In the times between trying the fireplace, the pipe between your outside tank valve and the indoor fireplace valve filled with propane. Then, when you opened the fireplace, this stored gas lit the flame. But, because the outside valve was only cracked, the pipe's pressure quickly decreased until the flame went out. Lather, rinse, repeat. – Daniel Griscom Mar 3 '17 at 21:12
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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.

  • I don't believe this is a case of correlation equaling causation. – BMitch Dec 25 '13 at 12:26
  • For water from a water line break to enter the gas piping this would be impossible. If that was the case with water able to enter the gas piping you would have a severe gas leak. – user31528 Jan 10 '15 at 2:14
  • @user31528 - Where I'm from, NG is run at a much lower pressure than H2O; entirely possible. – Mazura Jan 23 '16 at 23:09
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It's a log lighter not a gas fire. It'd used to assist in lighting wood logs. That's why it burns for a short time and then shuts down. It's designed for that purpose. It's doing exactly what its supposed to do. It's the operators misconception of what he has.

  • This is clever, but I doubt it's the situation here, as the original poster said the fireplace was working two weeks ago (relative to question date) – Chris Cudmore Sep 23 '16 at 16:49
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Here's what worked for me: I used a straw and blew out the little holes on top of the thermocouple and also around the pilot light.

Mine has been working for 24 hours now! Try first before anything else.

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This just happened to me and I opened the glass door, lit the fire to use the house air supply to keep the flame lit long enough to warm the flue liners then closed the door and voila. I left the door open for a couple of minutes.

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I'm sorry to say but obviously the first and most obvious solution to this problem is that the flame turns blue because it's running out of oxygen to burn I can almost guarantee being 20 years in the industry that in the two weeks between use something has built a nest, bird or flying insect such as bees have found a nice home in your air intake or perhaps if you have had a rodent enter from the outside they have built a perfect dwelling in the nice dry warm air intake

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    Hello, and welcome to Stack Exchange. I'm pretty sure that a flame low on oxygen turns yellow due to the unburned hydrocarbons (soot). – Daniel Griscom Mar 12 '17 at 12:49

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