Why does my gas fireplace flame turn blue then go out?

Author: Graciela Jacobs II  |  Last update: Tuesday, September 30, 2025

When a flame is turned on, it may appear blue in color. This may be temporary and caused by a few factors: particles in the air such as dust, or an incomplete combustion, which refers to a possible lack of oxygen.

How do you fix a blue flame on a gas fireplace?

Turn your pilot on CPI and leave it there. Try turning on the unit tonight and see if that solved the issue. Once you have air circulation (air in & air out) that should allow the flame to burn, turning from blue to yellow in about 10 minutes but never lifting off burner. If that does not fix it, call your dealer.

Why is my gas fireplace flame going in and out?

Often a gas fireplace has a millivolt generator which is in the path of the pilot flame. It is about the size of an AA battery and is wired to the switch and gas valve. If the millivolt generator is old and weak, or if the pilot flame is weak and wavering, the main burner will go on and off.

Why does my gas fireplace have a small blue flame when off?

The little flame you see in your gas fireplace after you have turned it off is called a pilot light. A Standing Pilot Light runs constantly, whether your fireplace is on or off.

How do you fix a gas fireplace that won't stay lit?

You need to replace the thermocouple and thermopile . Basically the thermocouple senses the flame and keeps the pilot lit and the thermopile produces the voltage to open the gas valve . If the pilot doesn't stay lit it's your thermocouple . You need to replace the thermocouple as cleaning usually doesn't work .

Gas Logs: Flame Won't Stay On - Why?

How do I know if my thermocouple is bad on my gas fireplace?

Common Signs of a Failing Thermocouple

Here are some common indicators: Difficulty Lighting the Fireplace: If you struggle to light your fireplace, or if it takes several tries to keep the pilot lit, it could suggest that the thermocouple is not sensing the flame correctly and is failing to keep the gas supply open.

Why won t my fireplace fire stay lit?

Firewood won't stay lit if it's made from softwood. Hardwoods include oak, birch, beech and maple, all dense enough to keep uncannily hot fires going for many hours. Oak is the densest of the hardwoods, generating the most heat for the longest time.

Is a blue gas flame OK?

A blue color when gas is burning indicates a properly burning flame. This means that the gas is burning at the color it was designed to. You may see a yellow tip of color at the top of the flame, indicating that the temperature is dropping as the flame glows higher.

Why does my gas fire go out after 20 minutes?

Poor ventilation can affect the flame as the vents become dirty or blocked, preventing sufficient airflow. It can disrupt the balance of oxygen and pressure needed for stable combustion, activate safety mechanisms, and lead to incomplete combustion and overheating, all of which can cause a gas fire to go out.

How much to replace a thermocouple in a gas fireplace?

Fireplace thermocouple replacement costs $150 to $350 total.

What is the most common problem with a gas fireplace?

One of the most common problems faced by homeowners with gas fireplaces is the pilot light going out or not staying lit. The pilot light is a small flame that ignites the gas burner, which produces the heat for your fireplace — if the pilot light goes out, your fireplace won't work.

Why does my gas fireplace flame go up and down?

A variety of burner problems can develop in a gas fireplace, leading to issues like a flickering flame or flame that gets too tall. Insufficient voltage, a failing thermocouple or malfunctioning thermostat are common causes of flickering burners. The burner or pilot may be dirty.

Why does the flame keep going out on my gas fireplace?

Your gas fireplace could be turning off for several reasons. The most like culprits are likely tied to some kind of problem with your setup. Anything from issues with your pilot light, clogged ports on burners, damage to heating components, and thermocouple/thermopile malfunctions can be to blame.

What happens when a flame turns blue?

Natural gas itself is a colourless gas whilst a natural gas flame burns with a blue colour. Gas that burns with a blue flame includes pure hydrocarbons like methane (refined natural gas), propane, butane and ethane. These gases come from raw natural gas processing and oil refining.

When should I be worried about a gas fireplace?

You start smelling strange odors

This smell should go away after three to four hours of use. A dirty fireplace with excessive pet hair or dust can also produce an odor. If you smell rotten eggs, call for help immediately, as you likely have a gas leak.

How do I know if my thermocouple is dirty?

Once you've located the thermocouple, do a visual inspection. You're looking for a few things. The first is signs of contamination on the tube, which can include discoloration, cracks, or pinholes. Next, check the wiring for any signs of wear or corrosion like missing insulation or bare wire.

How long does a thermocouple last on a gas fireplace?

Thermocouples can last up to 10 years if properly installed and maintained, while furnaces can last 15-20 years, although either may wear out sooner in multifamily units.

Why is my gas fireplace not staying lit?

So you've checked your pilot light and even reset it, but still, it wont stay lit. This can be an indication that your fireplace thermocouple is either bad or worn out. However, if your pilot is lit but the gas fireplace isn't, then there's probably a problem with your thermopile.

Why is my gas fireplace flame so blue?

A blue flame is caused by too much air mixed with the gas. In essence, it makes the burn too efficient.

Does a blue flame mean carbon monoxide?

Properly functioning gas appliances are quite safe. A blue flame is one indication of proper function and complete combustion. As discussed, malfunctioning units may generate carbon monoxide, due to incomplete combustion.

Which gas burns with blue flame?

Carbon monoxide burns with blue flame. In the presence of oxygen including atmospheric concentrations carbon monoxide burns with a blue flame producing carbon dioxide. When nitrogen gas burns, It has no color, odor or taste, and produces water when it burns in air.

Why does my gas fire go out after 15 minutes?

Thermocouple issues, pilot light problems, blocked venting systems, safety features, and gas supply issues are common reasons why gas fireplaces shut off.

Why does my gas fireplace keep turning off and on?

Sometimes, air trapped in the gas lines can cause a fireplace to suddenly shut off. This can be due to a restricted pilot light tube, incorrect gas pressure, or drafts that disturb the pilot light. Cleaning the pilot tube or adjusting the pilot flame may help.

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