What to Know About Gas Furnace Burners

A gas furnace is made up of many components, but none of these is more important than the gas furnace burner. This is where air and fuel is combined and burned in order to produce the heat that warms your home. Gases used in these types of gas burners are generally natural gas or liquefied petroleum gas.

The gas furnace burner is where the whole heating process really starts. Negative pressure is produced, which induces the flame to be drawn into the heat exchanger by the draft inducer. The flame’s combustion produces hot gases which pass through the heat exchanger, heating the walls and then the gas cools. In a high-efficiency furnace these gases are approximately 120 °F (50 °C) when they exit.

A gas furnace burner is normally placed on the floor of the furnace and fires in an upward direction. There are air registers which are located below the burner and movable flaps at the outlet of the blower which control the pattern and shape of the flame. If the flame gets out of control it could create flame impingement which is not good.

A gas furnace burner sometimes includes a pre-mixer which mixes the gas and the air to facilitate better combustion. There are various types of burners, and some use steam as the premix – they are called condensing furnaces. Condensing furnaces have efficiencies greater than 89%. Condensing furnaces deliver heat savings of between 20% and 35%.

In older style furnaces the burner is lit with a pilot flame, but modern furnaces usually use electronic ignition via an ignition transformer which works similarly to the spark plugs in a motor vehicle. The pilot light will in turn light the main flame. Natural gas is normally used to light the pilot light whilst the main flame can use both natural gas and diesel. When liquid fuels are used in a gas furnace burner, an atomiser is used so that the fuel does not just sink to the floor of the furnace and become a hazard.

The use of a pilot light to light the furnace is much safer than the old method of using a match. It is when this pilot light goes out or fails to ignite that you will experience one of the most common problems with your gas furnace. No pilot light, no heat, so understanding its workings and how to fix problems is important.

If you have a modern gas furnace burner, then the pilot light will be lit by an ignition transformer, but if you still have the old type of furnace, you stand a good chance of having the pilot light go out at some stage or other. In cases like this you will have no heat, so it is important that you know how to re-light the pilot light. Most gas furnaces will have instructions on how to light them, and if so you should follow the instructions. If not, here are some easy instructions on how to do it.

How to Light your Gas Furnace Burner

This is easier to accomplish with a long match or a wand lighter such as those used to light barbecues or candles.

  • Close the main gas line into your home.
  • Wait at least ten minutes for any residual gas fumes to dissipate.
  • Light your match or lighter wand and switch the gas valve on your furnace on to “pilot.”
  • While holding the lit match or wand to the pilot valve, press the red button alongside the dial.
  • Keep the button depressed for about one minute in order for the pilot to heat the thermocouple, allowing the gas valves to open.
  • Release the button and check to see whether the pilot light stays lit. If it does not remain lit wait for ten minutes again for the gas to dissipate and try once more.
  • Once the pilot light remains lit, turn the main gas line back on.
  • If the pilot stays lit but the burner doesn’t, call in the professionals, as you may need to have the thermocouple replaced.

A gas furnace burner will eventually get clogged up with dirt, dust and lint and will stop working effectively or fail to ignite at all. Because of this it is a good idea to know how to clean your burner, which should be done approximately every six months, dependent on use.

Gas Furnace Burners

How to clean your Gas Furnace Burner

You will need:

  • A vacuum cleaner
  • A tin or some other form of compressed air
  • A cloth to clean with.


  1. Switch off the burner and turn off the gas line which feeds the furnace.
  2. Open the main hatch to the furnace
  3. Vacuum the floor and dust the room so that no dust particles can get into the burner once you’ve cleaned it.
  4. Look under the firebox or heat exchanger to locate your burner.
  5. Vacuum the burner with a brush attachment in order to remove all lint and dust.
  6. Use the compressed air to blow any dust particles, dirt or lint out of the burner holes.
  7. Close the gas furnace burner hatch and switch the gas line and furnace back on.

Sometimes the flow of gas is not what it should be and this can be very unsafe. If the flow is not sufficient it can cause problems like too little heating or a spluttering flame. The flame in your gas furnace burner should never splutter or show any trace of yellow, it should be full and burn steadily. You can adjust the flame on the pilot light yourself by turning the flame adjustment screw which is usually located close to the gas valve on the pilot light assembly – the flame should be between 1.5 to 2 inches high. DO NOT attempt to adjust the flame on the main burner yourself – contact a professional to do this.

What you can check:

  • Make a mixture of water and liquid detergent
  • Paint gas supply line with the mixture, including all valves and connections. The mixture will bubble if there are any leaks.
  • If there is a leak, use a pipe wrench to tighten the connection, taking care not to over-tighten it.
  • If this does not help and there is still a gas leak, call in professional help.

Always be very careful when working on a gas furnace burner, and remember that you and your family’s safety is the most important factor. Always make sure that you switch off the gas supply to the furnace before attempting to make any gas furnace repairs or doing any maintenance.