Do you know how to light a furnace pilot light if it goes out? A pilot light is an essential component of some gas furnaces. It is responsible for igniting the burners at the beginning of heating cycles. Standing pilot lights are supposed to stay lit but occasionally go out due to airflow or gas supply issues. The furnace won’t heat up if the pilot goes out. Luckily, relighting the pilot is a simple process for homeowners to perform.
Most modern furnaces don’t include standing pilot lights. Instead, new furnaces use electronic ignitors to light the burners and initiate heating cycles. Like an extinguished pilot, a faulty ignitor prevents a furnace from heating up. Unlike pilots, electronic ignitors cannot be manually lit when they fail. However, a homeowner can take troubleshooting measures to determine if the ignitor is bad or if some other issue is causing the furnace not to blow hot air.
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Pilot Light vs Igniter
Standing pilot lights were standard in older furnaces but have been phased out because they waste fuel and are less safe and reliable than electronic ignition systems. Modern furnaces use electronic ignitors, which are more energy efficient and require less maintenance.
Standing Pilot Light
Furnaces manufactured before 2010 typically have standing pilot lights. A standing pilot consumes a steady fuel supply as the flame constantly burns, even when the furnace isn’t running. When the thermostat calls for heat, the pilot’s flame ignites the gas in the burners.
A pilot light system consists of a small burner, a gas valve, and a thermocouple. A thermocouple is a safety device that detects the presence of the pilot’s flame. The flame heats the thermocouple to produce an electrical current. The thermocouple transmits the current to the solenoid to keep the gas valve open. The current ceases if the flame goes out and the gas valve closes.
Electronic Ignition
Most furnaces manufactured after 2010 have electronically controlled ignition systems. Unlike pilot lights that burn constantly, electronic ignitions turn on at the start of the heating cycle. When the thermostat initiates a heating cycle, a current flows through the ignitor to light the gas in the burners.
The two main types of electronic ignition systems are hot surface ignitors and intermittent pilots.
Intermittent pilots use a high-voltage spark to ignite the pilot. An intermittent pilot burns fuel and lights the burners much like a standing pilot, but an intermittent pilot only burns when lighting the burners at the beginning of the heating cycle.
A hot surface ignitor is a metal resistance heating element, similar to a lightbulb filament. Unlike an intermittent pilot, a hot surface ignitor doesn’t consume fuel. An electric current runs through the ignitor’s metal until it is hot enough to light the gas in the burners. The ignitor shuts off when the furnace flame sensor detects the burner’s flames. Some hot surface ignitors also act as the flame sensor.
How to Light a Furnace with a Pilot Light
The furnace pilot light must be burning for the furnace to operate. If the pilot goes out, it must be relit. Relighting the pilot is simple. You will need a lighter or match with a long stem and a flashlight. If you are uncomfortable relighting the pilot, call a professional.
Step 1: Check the thermostat and pilot light.
Before anything else, check that the thermostat is working and has good batteries, and make sure the furnace’s electricity and gas supplies are on. If everything seems to be in order, check if the pilot light is burning.
The pilot resembles a small blue flame near the burners at the base of the furnace. The pilot light might be visible through a small window. It might be hidden behind the access panel if you can't locate the pilot. Before removing the panel, turn the furnace off with the switch on the side of the furnace or the breaker switch on the circuit panel.
After the power has been shut off, remove the access panel. Locate the main gas line, typically a dark metal pipe running into the furnace’s side. Follow the gas line to the furnace gas valve, a boxy component with a knob labeled “on,” “off,” and “pilot.” A knob or switch with only “on” and “off” labels indicates the furnace has an electronic ignition. See the section on electronic ignitions below for further instructions.
Locate a silver metal tube extending from the gas valve. This is the pilot tube, and it leads to the burners. Follow the line with your flashlight to the pilot nozzle at the end. Under regular operation, the pilot’s flame extends from the nozzle. If no flame is present, the pilot needs to be relit.
Step 2: Turn off the gas valve and wait five minutes.
Turn the gas valve’s knob to the “off” position. Wait five minutes for any residual gas to dissipate and for the furnace to cool before lighting the pilot. Accumulated gas is an explosion risk.
Step 3: Press or Hold Down the Reset Button
Automatic pilots automatically ignite by pressing the red reset button. Other pilots need to be manually ignited with a lighter or match. If the pilot doesn’t light automatically, hold the reset button or depress the valve knob, depending on the furnace model.
Step 4: Relight the pilot light
While pushing the reset button, bring the lighter or match to the end of the pilot nozzle to light it. Continue pressing the reset button for thirty seconds after the pilot lights to maintain gas flow and ensure the thermocouple heats up enough to open the main gas valve. When the pilot stays lit, gently release the reset button and turn the gas valve knob to “on.”
Step 5: Turn on your furnace and see if it works
Replace the access panel, and restore power to the furnace. If necessary, increase the thermostat’s temperature to get the furnace to kick on. If the burners don’t ignite, the thermocouple might not have heated up enough. Repeat the lighting procedure, holding the reset button for forty-five to sixty seconds after lighting the pilot.
How to Check/Test Gas Furnace with Electronic Ignition
Electronic ignitions cannot be lit. A faulty electronic ignition must be replaced, but you can try the following methods to determine if the ignitor is bad before replacing it or calling a professional.
Listen for Clicking
If you have an intermittent pilot or direct spark ignition, listen near the furnace for a clicking noise when the furnace turns on. These ignition systems produce sparks to light the burners and make audible clicking sounds. If your furnace repeatedly clicks and doesn’t produce heat, there is an issue preventing the ignitor from lighting the burners.
Observe Hot Surface Ignitor
If you have a hot surface ignitor, ensure its plug is connected and see if it glows at the beginning of the heating cycle. First, shut off the furnace switch on the side of the unit, and remove the furnace’s access panel. To locate the ignitor, follow the thick, black gas line pipe to the burners.
The ignitor is located on this side behind the burners and looks like a thin, flat, rectangular metal. Lower the thermostat’s temperature to initiate a heating cycle when you restore power to the furnace. Switch the furnace on, and watch the ignitor. After the inducer motor starts, you will hear the gas valve click open and gas hiss out. At this point, the ignitor should begin to glow red. If it doesn’t, there is an issue with it.
Inspect the Hot Surface Ignitor
Cut power to the furnace and let it cool for several minutes. Disconnect the ignitor's wire, carefully remove it, and don’t touch the filament. Ignitors are incredibly fragile and can break under a minimal amount of force. Check if the ignitor is singed or cracked. Even a microscopic crack will cause an ignitor to fail.
Test the Hot Surface Ignitor
If you own a multimeter, you can test the voltage or continuity of the hot surface ignitor. Test the voltage while the furnace is running. Touch the multimeter’s probes to the ignitor’s wires. The reading should be 120 volts. The ignitor is bad if there is voltage, but the furnace isn't igniting. If there’s no voltage, another component is bad.
Check the ignitor’s resistance with the furnace's power turned off. Set the multimeter to the lowest ohms of resistance. Unplug the ignitor and touch probes to each terminal. The multimeter will read between 30 and 200 ohms if there is continuity. If there is no reading or only a change, the ignitor is bad.
Check the Control Board Code
Most electronic ignition furnaces have control boards that indicate the causes of furnace failures with LED lights. The lights on the control board blink to reveal failure codes that can be deciphered with a chart located in the owner’s manual, on the access panel, or inside the furnace. The control board is typically located in the lower blower compartment.
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Troubleshooting Tips When Your Furnace Is Not Igniting
Try these additional troubleshooting tips if you can’t determine why your furnace isn’t igniting.
Check the Thermostat and Power Source
Ensure the thermostat is switched to "heat" and the temperature setting is lower than the room's temperature. Make sure the power switch on the side of the furnace is on. Check the circuit breaker panel for a tripped breaker switch.
Turn Your furnace off and on
Flip the lightswitch-looking toggle on the furnace or the circuit switch on the breaker panel to cut power to the furnace. Wait 30 seconds, and then restore power. Restarting the system might be enough to get your furnace running again.
Make Sure the Gas Valve Is On
Ensure the main gas line is open and the gas valve inside the furnace is switched on.
Check the Air Filters
Clogged air filters can trigger the limit switch to shut the furnace down. The limit switch shuts the furnace down when it senses excessive heat inside the furnace. Clogged air filters reduce airflow and can cause furnaces to overheat. Replace the air filter or filters; some systems have two filters. Energy.gov recommends that air filters are replaced once a month or as often as the manufacturer recommends. Air filters are easy to replace, but be sure you know which way the furnace filter goes.
Clean the Flame Sensor
A dirty flame sensor can prevent a furnace from heating. A flame sensor is a safety device that closes the gas valve if the burners do not ignite to prevent the house from filling with gas. A dirty flame sensor cannot sense heat from the burners and closes the gas valve. If it's dirty, clean the furnace flame sensor.
Call an HVAC Professional
Call a professional HVAC technician if the furnace won’t ignite after performing troubleshooting measures or if the furnace has persistent issues.
Conclusion
Furnaces use standing pilot lights or electronic ignition systems to light the burners. The furnace won't heat up if the pilot goes out or the ignitor fails. If an electronic ignition fails, it must be replaced to make the furnace operational. Several methods help you determine if the ignitor or something else is faulty, and the additional troubleshooting measures might be enough to get your furnace running again.
Frequently Asked Questions
Why does the pilot light go out on a gas fireplace?
Drafts, high winds, and improper venting can blow out pilot lights. A dirty pilot orifice, bad gas valve, or faulty thermocouple can cause a pilot to go out. Gas supply issues such as a bad gas regulator or high demand are two additional causes of extinguished pilots.
Where is the pilot light in a furnace?
The pilot is located near the burners at the base of the furnace. The pilot light might be visible through a small window. It might be hidden behind the access panel if you can't locate the pilot.
Before removing the panel, turn the furnace off with the switch on the side of the furnace or the breaker switch on the circuit panel. Remove the access panel, and find the gas control valve with a knob labeled on, off, and pilot. The pilot tube is the small silver tube that leads from the valve to the burner. Follow the pilot tube to the nozzle at the end. This nozzle is where the flame burns. If the pilot is lit, you will see a blue flame from the pilot's nozzle in the burner.
Where is the ignitor on a furnace?
The ignitor is located near the burners. Turn off the power to the furnace and remove the access panel. Follow the black gas line from the gas valve to the burners. The ignitor is located on this side behind the burners.
A spark ignitor looks like a metal probe with a cylindrical ceramic housing. A wire is attached to the other end of the ceramic tube. The flame sensor may be attached to the same assembly. A hot surface ignitor looks like a rectangular, flat piece of metal with rectangular or cylindrical ceramic housing and two wires attached to the other end of the ceramic.
