Should the Pilot Light Always Be ON in a Gas Furnace?

During the summer, a common concern among homeowners is whether the pilot should be ON throughout or put out when heating is done. On one side, the experts say that you should leave the pilot light ON throughout as it’s safer that way. However, on the other side are concerned homeowners who feel leaving the pilot ON even when the furnace is OFF is unnecessarily expensive. So, who is correct? 

Yes. Ideally, the pilot light should be ON in a gas furnace throughout the heating season. Although it costs a little more to keep the pilot light ON round the clock, the benefits typically outweigh the downsides. 

Should You Turn Furnace Pilot Light OFF in Summer

No, it’s advisable to shut off the furnace pilot light in the summer when you don’t need heating. The only time you should leave the pilot light ON round the clock is during the winter when you essentially need heating throughout. Failure to put out the pilot light flame during the summer can leave you with an unnecessary power bill.

Remember that the pilot light consumes around $500 worth of fuel over 12 months. So, not turning it off during the summer can easily leave you with a bill close to $320 bill or more. You can save that money by turning off the pilot. Additionally, keeping the pilot light in the summer when you don’t need heating is an unnecessary safety risk, as we’ll find out shortly. 

What is Pilot Light on a Gas Furnace? 

Let’s take a step back to understand better the role of the pilot light on a gas furnace and why keeping it ON or OFF is a big deal. The pilot light is a small blue flame used to ignite the burners in your gas furnace, which in turn provides the flames necessary to heat your home. A standard pilot light gets fuel via a small tube attached to the line feeding your burners.

It also features a safety valve, known as a thermocouple, to stop the gas flow if the pilot light goes out. A proper pilot flame is blue with a small yellow at the tip. It should also be strong enough to cover about ½ of the thermocouple tip.  

How the Pilot Light Works

The way a pilot works is simple. Pilot lights feature a small tube that allows a small amount of gas to come out and keep the light burning. You need to light it manually with a match if the flame goes out. 

If everything goes to plan, the pilot flame remains on throughout to repeatedly light your burners whenever you turn on the furnace. This way, you don’t have to worry about lighting the burners manually or lighting the pilot flame each time you need heating. 

An electric thermocouple consistently tracks the pilot flame to ensure that the furnace isn’t pushing gas out of the pilot valve with no flame, as this can cause gas poisoning. Thermocouples are electrical devices that convert heat to electric voltage. Thus, the pilot light thermocouple can quickly tell whether the furnace flame is ON or OFF and shut down the appliance accordingly. 

How? It’s simple. In the pilot light, one of the thermocouple junctions sits in the pilot light flame, generating electricity that keeps a small electromagnetic valve open. This is the valve that lets gas flow to the pilot light. If the pilot light goes off, the thermocouple quickly cools down, stops producing electricity, and thus the valve closes, instantly cutting the gas supply. 

Do All Furnace Have a Pilot Light?

Technically, no. All furnaces have a pilot light system to ignite the burners. However, not all furnaces have a constantly present pilot light flame. So, no, you won’t find a lit pilot flame in all furnaces. Only older, traditional furnaces have this type of pilot light. Newer furnaces have “smarter” ignition systems that don’t rely on a constantly burning pilot flame.

Modern vs. Older Furnace Models

Older furnaces use a standing pilot that remains ON throughout the heating season. You need to light the pilot flame when starting the furnace for the first time during the winter season – we’ll discuss how to light the standing pilot shortly. It remains lit once it is on until you shut down the furnace at the end of the winter season. 

Meanwhile, modern furnaces are fitted with innovative ignition systems that only light the pilot when the thermostat calls for heating. So, the flame stays out until your indoor temperatures drop below the thermostat setting. Modern furnace ignition systems fall into two broad categories – intermittent pilot lights and hot-surface ignition systems. Intermittent pilot lights use a spark plug that combusts spontaneously when exposed to high-temperature gas.

Meanwhile, hot surface ignition systems use silicon carbide igniters instead of regular spark plugs. When the thermostat calls for heating, the furnace sends low-voltage, high current electricity through the igniter, causing it to become red hot, typically at 2500°. Once the igniter is glowing hot, the furnace opens the pilot gas valve, causing the pilot system to ignite spontaneously. 

How Do I Know if My Furnace Has a Pilot Light?

Generally, you know that your furnace has a standing pilot light if you come across a round knob with the words OFF/ON/PILOT on the furnace. You can also remove the front panel and look inside the furnace to confirm. You’ll see a blue flame inside the burner area if you have a traditional standing pilot furnace. 

Where is Pilot Light on a Furnace?

The pilot light is located within the burner assembly inside your furnace. To access it, remove the access cover to access the burner assembly. Then look toward the bottom. You’ll see a dial (usually red) that says “ON,” “OFF,” and “PILOT.” This is the gas valve knob we mentioned earlier. 

Now, note the three tubes attaching to the base of the gas valve housing. The larger tube feeds the burners while the two smaller ones lead to the pilot. One supplies the pilot itself and the other the thermocouple. The pilot orifice is located at the end of the pilot tube. Alternatively, you may notice a small blue flame within the burner assembly if the pilot light is ON. 

Should the Pilot Light Always Be ON in a Gas Furnace?

Ideally, yes. You should leave the pilot light ON throughout the heating season. It’s safer and more economical in the long run. That said, though, keeping the pilot light throughout also comes with a few drawbacks. The following pros and cons should help you make an informed decision. 


  • Prevent spider webs: Spider webs are attracted to a compound known as mercaptan that gas companies add to gas as an odorant. Therefore, turning off the pilot flame can invite spiders to build webs around and inside the pilot tube, potentially causing a blockage.
  • Keep moisture out: We all know the dangers of exposing your gas lines to water or moisture. Moisture causes gas to burn less efficiently and freeze, thus blocking gas lines. Unfortunately, blowing out the pilot light leaves the pilot area (including the orifice) exposed to the summer’s high humidity levels. Leaving the flame ON can help prevent moisture buildup.


  • Adds to indoor heat: Although the pilot light is a small flame, it’s heat nonetheless. This might not be a very good thing in the summer when you’re already trying to remove heat from the house. It means your air conditioner has to work even harder. 
  • Higher energy bills: Keeping the pilot light ON round the clock, even during the summer, can add to your energy bills in two main ways. First, as we’ve seen, your air conditioner will need to work extra hard to keep you cool, meaning higher power bills. Additionally, the pilot flame itself depends on gas to stay on, meaning even more energy bills. 
  • Increased maintenance needs: Finally, leaving the pilot light ON throughout means you now also need to worry about furnace maintenance in addition to air conditioner maintenance. For instance, you need to wipe the unit regularly to prevent soot buildup and potential corrosion of components.  

Is It Bad to Turn your Furnace ON and OFF?

Yes, turning your furnace on and off repeatedly is rarely a good idea. Granted, you should turn it off when the warmer weather sets in. However, turning it off merely because you’re away for the night and back on when you return home is not good practice.

Why? There are a couple of reasons. First, frequent restarts accelerate wear and tear, meaning increased repair frequency. Secondly, turning the furnace off and back on after a short while often leads to energy wastage. This is because it takes more power (gas and electricity) to raise a furnace to the previous thermostat setting than maintain the setting. 

Above all, turning the furnace off merely because you’re going away for a night or two puts your home at significant risk of frozen pipes and consequential water damage. Both can be very expensive. 

Reasons your Furnace Pilot Light Keeps Going Out and How to Fix Them

Let’s now discuss why your furnace may go off (accidentally), how to fix them, and how to relight your pilot light.

How to Tell if your Pilot Light is Out in the Furnace

One of the first signs that your pilot light is out (for standing pilot systems) is when the furnace isn’t kicking on. Alternatively, you can check inside the burner compartment. If the burners won’t come on, the pilot light is likely out no matter how many times you start the furnace. 

The good news is that you can peek inside the pilot area too. You should see a strong blue flame if the pilot light is lit. Otherwise, it’s out. 

What Happens if the Pilot Light Goes Out on a Furnace?

First off, the burners won’t light, meaning you cannot get heat from the furnace. Secondly, the pilot thermocouple will shut the valve leading to the pilot orifice to prevent gas buildup within the furnace and in your home. Finally, a broken pilot light can also cause furnace lockout, necessitating a manual reset. 

How to Light Furnace Pilot when Needed

  1. Turn off the gas at the main valve.
  2. Remove the furnace’s access door to access burner assembly
  3. Locate the pilot knob (with ON/OFF/PILOT markings)
  4. Set the knob to “PILOT”
  5. Light the pilot flame using a match while pressing the reset button or depressing the knob.
  6. Wait for the pilot flame to stay on for 30 seconds, then slowly release the button or knob.
  7. Set the gas valve to “ON.”
  8. That’s all!

How to Turn OFF Pilot Light on Gas Furnace

  1. Turn the mode on the thermostat from “HEAT” to “OFF” or “COOL.”
  2. Locate the knob with “ON/OFF/PILOT” markings in your burner assembly and set it “OFF.”
  3. Rotate the gas valve on the intake pipe to turn it off.
  4. That’s all!

Reasons your furnace pilot light keeps going out and how to fix

The three main reasons your light won’t stay lit are thermocouple issues, a filthy pilot orifice, and poor location. Here’s how to fix each:

  • Broken/bent/dirty thermocouple: Begin by cleaning the thermocouple with fine grain sandpaper. Then straighten it and return it to the burner assembly. If it still doesn’t work, replace it. 
  • Filthy pilot orifice: Shut down the furnace and use a thin needle to remove the dirt clogging the opening. Poor location: Call a professional as furnace location is a delicate matter. Moreover, you must keep ventilation in mind.


Do all gas furnaces have a pilot light? Technically, no. Only traditional models have a standing pilot light. However, all gas furnaces have a pilot system. 

Do new furnaces have pilot lights? No, modern gas furnaces don’t have a pilot light. Instead, they use an intermittent pilot or hot surface ignition systems. 

When did furnaces stop using a pilot? New gas furnaces stopped using standing pilot lights circa 2010 when the first intermittent pilot system was developed. 

Does a furnace pilot light always stay on? In winter, yes. It’s more convenient and less costly to keep the furnace ON during winter. However, you’re allowed to shut down your furnace to save on costs during the summer. 


The pilot light is a critical part of the gas furnace, without which the furnace wouldn’t work. Therefore, you need to understand it better and take the best care of it. Now you know how to set it, light it, put it off, and even clean your pilot light.