Most gas furnaces built before 2005 have a pilot light, but newer models use electronic ignition instead
A pilot light is a small, continuously burning flame that ignites the main burner when your furnace needs heat. If your furnace was installed before the mid-2000s, it almost certainly has one. Newer furnaces use electronic ignition systems — they create a spark or hot surface to light the burners on demand, then shut off when heating stops. The age of your furnace is the quickest way to know which type you have.
Pilot lights are reliable but wasteful. They burn constantly, even in summer when you don't need heat, using gas continuously. Electronic ignition systems are more efficient because they only use energy when the furnace actually fires up. This shift happened gradually through the 1990s and 2000s, so furnaces from that transition period vary.
You can tell which system your furnace uses by looking at it. If you see a small blue flame burning steadily inside the furnace cabinet (usually visible through a small window or opening), you have a pilot light. If you don't see any flame, or if you only see flames when the furnace is actively heating, you have electronic ignition.
Key Takeaways
- Furnaces made before 2005 typically have pilot lights that burn continuously; newer furnaces use electronic ignition that only fires when needed.
- A pilot light is a small, steady blue flame you can usually see through an opening in the furnace cabinet.
- Pilot lights go out occasionally and need to be relit by hand, while electronic ignition systems restart automatically.
- Pilot light furnaces waste more gas than electronic ignition models because the flame burns all the time.
- If your furnace has a pilot light and it goes out, you can often relight it yourself by following the instructions on the furnace door.
How a pilot light works in a gas furnace
The pilot light sits near the main burner and burns a small amount of gas continuously. When your thermostat calls for heat, a valve opens to send gas to the main burner. The pilot flame ignites that gas, and the main burner roars to life with a much larger flame. Once the furnace reaches the target temperature, the thermostat shuts off the gas valve, the main burner stops, and the pilot light stays on, waiting for the next heating cycle.
The pilot light is held in place by a small tube called a pilot tube, which delivers gas to the flame. A safety device called a thermocouple sits in the pilot flame and generates a tiny electrical signal that tells the furnace the pilot is lit. If the pilot goes out, the thermocouple stops sending that signal, and the gas valve closes automatically — this prevents unburned gas from flooding into your home.
This design is straightforward and has no moving parts in the ignition system, which is why pilot light furnaces are so durable. The downside is that the pilot flame wastes gas year-round, even during months when you don't need heat.
Electronic ignition systems in newer furnaces
Modern furnaces use one of two electronic ignition methods: hot surface ignition or spark ignition. In hot surface ignition, an electric heating element glows red-hot when the furnace fires up, and the gas ignites when it reaches that hot surface. In spark ignition, an electric spark plug creates a spark that lights the gas, similar to how a car engine starts.
Both methods save energy because they only operate when the thermostat calls for heat. The furnace control board powers the ignition system, waits for a flame sensor to confirm the burner is lit, and then shuts everything down when heating is complete. If the ignition fails, the control board detects it and locks out the furnace to prevent gas from building up.
Electronic ignition systems are more complex than pilot lights — they have more components that can fail — but they are far more efficient. A furnace with electronic ignition uses roughly 10 to 15 percent less gas than an identical furnace with a pilot light, because there is no continuous flame burning when you don't need heat.
When a pilot light goes out and how to relight it
Pilot lights can go out for several reasons: a draft blowing out the flame, a clogged pilot tube, a faulty thermocouple, or straightforward age. When it goes out, your furnace will not heat, and you will see no flame when you look into the furnace cabinet. The good news is that relighting a pilot light is often something you can do yourself.
Most furnaces have instructions printed on the inside of the access door or on a label near the pilot light. The typical steps are: turn the gas control knob to "Off" and wait five minutes, then turn it to "Pilot." Hold a long lighter or match near the pilot tube opening while pressing and holding the ignition button. Once the pilot lights, keep holding the button for 30 to 60 seconds so the thermocouple heats up and registers the flame. Then turn the knob to "On" and listen for the main burner to ignite on the next heating cycle.
If the pilot will not stay lit after you relight it, or if it goes out repeatedly, the thermocouple or pilot tube may be dirty or damaged. At that point, you should call a furnace technician. Attempting to repair the thermocouple or pilot tube yourself can be dangerous if you are not familiar with gas appliances.
Advantages and disadvantages of pilot light furnaces
Pilot light furnaces are extremely reliable and straightforward. They have fewer electronic components, so there is less that can break. They will continue to work even if the power goes out, as long as you can relight the pilot manually. They are also less expensive to repair when something does go wrong, because replacement parts are inexpensive and widely available.
The main disadvantage is energy waste. A pilot light burns roughly 400 to 600 BTUs of gas per hour, 24 hours a day, 365 days a year. Over a heating season, that adds up to a noticeable increase in your gas bill compared to a furnace with electronic ignition. If you live in a mild climate where you only heat for a few months, the waste is smaller. If you heat for eight months or longer, the cost difference becomes significant.
Pilot light furnaces also require occasional maintenance. You may need to relight the pilot yourself if it blows out, and the thermocouple and pilot tube can become clogged with dust or debris over time. Electronic ignition systems are more self-sufficient — they restart automatically and do not require manual relighting.
Should you replace a pilot light furnace with electronic ignition
If your furnace is 15 to 20 years old and still working, replacing it with a new furnace that has electronic ignition will lower your heating costs. A new furnace is also more efficient overall — modern furnaces have better insulation and burner design than older models, so you save money beyond just eliminating the pilot light waste.
The trade-off is the upfront cost of a new furnace, which typically ranges from several thousand dollars depending on your region and the size of your home. You will recover some of that cost through lower gas bills over time, but the payback period is usually 10 to 15 years. If your current furnace is still heating reliably, you may decide to keep it until it fails.
If your pilot light furnace breaks down and repair costs are high, that is often a good time to replace it. A new furnace with electronic ignition will be more reliable, more efficient, and will not require you to relight a pilot in the middle of winter.
Frequently Asked Questions
Can I convert my pilot light furnace to electronic ignition?
No, you cannot retrofit electronic ignition into a pilot light furnace. The control boards, gas valves, and ignition components are completely different, and the cost of replacing all of them would be nearly as much as buying a new furnace. If you want electronic ignition, you need to replace the furnace.
Is it dangerous if my pilot light goes out?
No, it is not dangerous. The thermocouple automatically shuts off the gas valve when the pilot goes out, preventing unburned gas from entering your home. Your furnace straightforward will not heat until you relight the pilot or call a technician.
How often should a pilot light need relighting?
A healthy pilot light should stay lit indefinitely. If you are relighting it more than once or twice a year, the thermocouple, pilot tube, or gas valve may be faulty and should be inspected by a technician.
Do pilot light furnaces work during a power outage?
Yes, the pilot light itself does not require electricity. However, the furnace blower (the fan that pushes warm air through your home) will not run without power, so you will have a flame but no heat circulation. Electronic ignition furnaces will not work at all during a power outage.
What does it mean if my pilot light is yellow or orange instead of blue?
A yellow or orange flame usually means the pilot tube is partially clogged with dust or debris, restricting airflow to the flame. This can cause the pilot to go out more easily. You should have a technician clean the pilot tube. Do not attempt to clean it yourself, as the gas valve and pilot assembly require careful handling.