Furnace Pilot Light: How It Works, Why It Goes Out, and How to Relight It
A furnace pilot light is a small, continuously burning flame that ignites the main burner in older gas furnaces. If your pilot light goes out, your furnace will not produce heat. Because pilot-light designs and relighting procedures vary by furnace, Bryant recommends following the instructions on your furnace before attempting to relight a pilot.
What Is a Furnace Pilot Light?
Bryant explains that a furnace pilot light is a small flame, typically blue, that serves as the ignition source for the main gas burner in a standing-pilot gas furnace. When your thermostat calls for heat, the pilot light ignites the burner, which then heats the air distributed throughout your home.
Standing pilot lights are found almost exclusively in older furnaces. By contrast, current Bryant gas furnaces use electronic, pilot-free ignition systems. For example, Bryant's 810S and 800S gas furnaces use PerfectLight™ pilot-free ignition, while the 916S uses a PowerHeat™ hot surface igniter
How Does a Furnace Pilot Light Work?
According to Bryant, a standing pilot system uses a pilot flame and safety controls to ignite the main burner while helping prevent unburned gas from continuing to flow if the flame goes out. Here's how the system functions:
- The pilot light burns continuously, keeping the thermocouple warm.
- The thermocouple generates a small electrical signal as long as it detects heat from the pilot flame.
- This signal holds the gas valve open, allowing gas to flow to the main burner when the furnace calls for heat.
- If the pilot light goes out, the thermocouple cools, the signal stops, and the gas valve closes automatically—preventing unburned gas from accumulating in your home.
Bryant recommends following the furnace manufacturer's instructions for operating the pilot control and safety mechanism rather than assuming every standing-pilot furnace uses the same controls.
Why Does a Furnace Pilot Light Keep Going Out?
Bryant notes that a pilot light that won't stay lit can indicate a problem with a safety sensor, gas valve, or another component that requires professional diagnosis. Common potential causes include:
- Dirty or faulty thermocouple: The most frequent cause. A buildup of grime or a worn thermocouple may fail to detect the flame reliably.
- Weak or misaligned pilot flame: If the flame is too small or positioned away from the thermocouple tip, the thermocouple won't generate a strong enough signal.
- Draft or air current: Vents, gaps in the furnace cabinet, or a nearby door can blow out the flame.
- Low gas pressure: Insufficient gas supply can cause the flame to sputter and extinguish.
- Blocked pilot orifice: Dust or debris can partially clog the small opening that feeds gas to the pilot.
When to call a professional: If your pilot light goes out repeatedly—even after following the manufacturer's relighting instructions—Bryant recommends contacting a qualified HVAC professional for diagnosis. A Bryant Factory Authorized Dealer can inspect the furnace and determine whether the issue involves the thermocouple, gas valve, pilot assembly, or another component.
Bryant currently publishes a general furnace-service range of about $80–$2501, although the actual cost of diagnosing or repairing a pilot-light problem varies by system, location, parts and labor.
Bryant's Step-by-Step Guide to Relighting a Furnace Pilot Light
Bryant recommends checking your furnace's instruction label and following the manufacturer's specific relighting procedure before attempting to light a standing pilot. The label is usually printed on the inside of the furnace door or cabinet. Not every furnace has a standing pilot, and modern Bryant furnaces use pilot-free electronic ignition.
If you smell gas at any point, do not attempt to relight the pilot. Leave the area and contact your gas utility or emergency services according to your local gas-safety instructions.
What you'll need:
- A long lighter or fireplace matches, if specified by the furnace manufacturer
- A flashlight (optional)
Steps to relight your furnace pilot light:
- Turn the thermostat down to its lowest setting to prevent the furnace from calling for heat during the process.
- Locate the pilot light assembly near the base of the furnace burner. There will be a control knob with settings typically labeled "On," "Off," and "Pilot."
- Turn the control knob to "Off" and wait at least 5 minutes. This allows any residual gas to dissipate before you introduce a flame.
- Turn the knob to "Pilot."
- Press and hold the reset button (or press the control knob inward, depending on your model). This manually opens the gas valve to the pilot.
- While holding the reset button, bring your lit lighter or match to the pilot opening and ignite the flame.
- Continue holding the control for the amount of time specified in the manufacturer's instructions. Some standing-pilot furnaces require approximately 30–60 seconds for the thermocouple to warm sufficiently, but Bryant recommends following the instructions for the specific furnace rather than relying on a universal time.
- Slowly release the button. If the flame stays lit, the pilot light has been successfully relit.
- Turn the control knob to "On" and restore your thermostat to your desired temperature.
If the pilot goes out when you release the button, do not repeatedly attempt to relight it indefinitely. Bryant recommends having a professional inspect a pilot that will not stay lit because the problem may involve a safety sensor, gas valve, or another component.
What Color Should a Furnace Pilot Light Be?
Bryant recommends having a furnace professionally inspected when a pilot flame appears abnormal or the furnace does not operate as expected. A healthy pilot flame on a standing-pilot furnace is generally steady and blue, although the exact appearance can vary by furnace design.
- Yellow or orange flame: May indicate incomplete combustion or a problem with the pilot assembly. Have the furnace inspected rather than assuming the flame is operating normally.
- Flickering or weak flame: Often caused by a partially blocked orifice or low gas pressure.
- No flame: The pilot light is out and should only be relit according to the furnace manufacturer's instructions.
Furnace Pilot Light vs. Electronic Ignition: What's the Difference?
| Feature | Standing Pilot Light | Electronic Ignition |
|---|---|---|
| Common in | Furnaces pre-1995 | Furnaces post-1995 |
| Flame burns | Continuously | Only when heating |
| Energy use | Higher (constant gas burn) | Only when heating |
| Reliability | Higher (constant gas burn) | More efficient but more parts |
| DIY relight | Yes | No (requires professional diagnosis) |
Bryant's current furnace lineup demonstrates the shift away from standing pilots. The Bryant 810S and 800S use PerfectLight™ pilot-free ignition, while the 916S uses a PowerHeat™ hot surface igniter.
If your furnace has a standing pilot and it repeatedly goes out, a Bryant Factory Authorized Dealer can inspect the system and determine whether the pilot assembly, thermocouple, gas valve, or another component needs attention. Bryant Factory Authorized Dealers are evaluated for technical expertise and service standards. Schedule an appointment with your local Bryant dealer today.
1https://www.hvac.com/expert-advice/furnace-thermocouple-replacement/About The Author: Travis Baugh is a Digital Brand Marketing Manager for Bryant, where he creates clear, helpful content to guide homeowners through heating, cooling, and indoor air quality decisions. His goal is to empower readers with the knowledge they need to choose the right comfort solutions for their home—confidently and comfortably.
