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Furnace Pilot Light: What It Is, Why It Goes Out & How to Fix It 


Your furnace pilot light is a small flame that allows your furnace to ignite and heat your home. When it goes out, your furnace stops working completely. This guide breaks down everything homeowners in Cupertino need to know about pilot lights, common causes of failure, troubleshooting tips, and repair costs.
For fast furnace repair, call HVAC Cupertino at (408) 740-7079.

1. What Is a Furnace Pilot Light?A furnace pilot light is a small, continuously burning flame located near the burner assembly. Its job is simple:

• Light the main burners
  
• Allow the furnace to ignite safely
  
• Ensure proper gas combustion
  

Older gas furnaces rely on a standing pilot flame, while newer furnaces use electronic ignition instead of a constant flame.

2. How Do I Know If My Furnace Has a Pilot Light?You likely have a pilot light if:

• Your furnace is over 20 years old
  
• There is a small access door near the burner
  
• You see a small blue flame when looking inside
  
• Your instruction label mentions “pilot,” “pilot assembly,” or “thermocouple”
  

Most modern high-efficiency furnaces do not use pilot lights—they use hot-surface igniters or spark igniters.

3. What Color Should a Furnace Pilot Light Be?A healthy pilot flame should be:

• Blue
  
• Steady
  
• Strong enough to touch the thermocouple (the small metal safety sensor tip)
  

A yellow, flickering, or weak flame indicates a problem such as:

• Gas supply issues
  
• Dirty pilot orifice
  
• Drafts
  
• Failing thermocouple
  

4. Why Does My Furnace Pilot Light Keep Going Out?This is one of the most common furnace issues. Here are the primary causes:
• Drafts or Airflow IssuesWind or indoor drafts can blow out the flame.
• Dirty Pilot OrificeDust or debris can restrict gas flow.
• Bad ThermocoupleA thermocouple that fails to detect heat will shut off the gas supply.
• Low or Unstable Gas PressureCauses a weak, unstable flame.
• Cracked Heat Exchanger (Rare but serious)This creates backdraft conditions that extinguish the flame.
• Faulty Gas ValveGas valve issues can prevent the pilot from staying lit.
If your pilot light goes out repeatedly, call for service at (408) 740-7079.

5. How Do I Relight a Furnace Pilot Light? (Safe Step-by-Step)Most standing pilot furnaces follow the same process.
Always check your furnace label and follow manufacturer instructions.
How to Relight It:

1. Turn the gas knob to OFF.
   
2. Wait 5 minutes to clear unburned gas.
   
3. Turn the knob to PILOT.
   
4. Press and hold the reset or ignition button.
   
5. Light the pilot with a long lighter while holding the button.
   
6. Continue holding the button for 30–60 seconds.
   
7. Turn the knob to ON once the flame is stable.
   

If the flame goes out again, the thermocouple is usually the problem.

6. How Do I Know My Thermocouple Is Bad?A bad thermocouple prevents the pilot light from staying on.
Signs include:

• Pilot lights but won’t stay lit
  
• Pilot flame is strong, but shuts off anyway
  
• Furnace attempts to start but fails
  
• You have to hold the pilot button down for too long
  

Thermocouple replacement normally solves the issue.

7. Can a Pilot Light Leak Gas?Not when functioning properly.
But if the gas valve or pilot assembly malfunctions, gas may continue flowing after the flame goes out.
You may smell:

• Rotten egg odor
  
• Sulfur smell
  
• Faint gas around the furnace
  

If you smell gas:

• Turn furnace OFF
  
• Open windows
  
• Exit the home
  
• Call your gas provider
  
• Contact HVAC Cupertino immediately
  

Never ignore gas odors.

8. How Much Does It Cost to Fix a Pilot Light?Repair costs vary based on the cause:
• Pilot Cleaning:$75 – $150
• Thermocouple Replacement:$100 – $300
• Gas Valve Replacement:$300 – $750
• Flame Sensor or Igniter Issues (modern units):$120 – $450
In Cupertino, most pilot-related repairs average $150–$350.

9. Should a Pilot Light Always Stay On?If you have a standing pilot furnace, yes.
A continuously burning flame is required for ignition. However, if your pilot goes out frequently, the system needs cleaning or repair.
If you have an electronic ignition furnace, there is no standing flame.

10. What Does It Mean If My Pilot Flame Is Yellow?A yellow or orange flame can indicate:

• Dirty burner
  
• Improper combustion
  
• Gas pressure issues
  
• Carbon monoxide risk
  

This is a safety concern—turn off your furnace and call a professional.

11. Is It Safe to Relight a Pilot Light Myself?Yes—if you follow instructions carefully.
But it is not safe when:

• You smell gas
  
• Pilot won’t stay lit
  
• You’ve relit it several times
  
• There is soot or discoloration
  
• The flame looks weak or unstable
  

If unsure, call a licensed technician at (408) 740-7079.

12. Can a Dirty Furnace Cause the Pilot Light to Go Out?Absolutely. Dust and debris can clog:

• Pilot orifice
  
• Burners
  
• Heat exchanger
  
• Draft hood
  

Annual furnace maintenance helps prevent these issues.

13. Should I Replace a Furnace With Pilot Light Ignition?Standing pilot furnaces are typically older, often 20–40 years old.
Consider replacement if:

• Pilot goes out frequently
  
• Furnace needs repeated repairs
  
• You have high winter energy bills
  
• Your system is older than 20 years
  
• Your home has uneven heating
  

Newer furnaces use electronic ignition, which is more efficient and reliable.

14. How Long Do Pilot Lights and Thermocouples Last?

• Pilot lights: Last as long as furnace is functional
  
• Thermocouples: 5–10 years
  
• Furnace lifespan: 15–25 years
  

If your furnace is over 20 years old, upgrading may be more cost-effective than frequent repairs.

15. When Should You Call a Professional?Call an HVAC technician if:

• Pilot light won’t stay lit
  
• You smell gas
  
• Flame is yellow
  
• Furnace keeps shutting off
  
• Resetting pilot doesn’t work
  
• Furnace is old and inefficient
  

These issues often require specialized tools and safety checks.

Need Furnace Repair in Cupertino? Call (408) 740-7079At HVAC Cupertino, we provide:

• Pilot light repair & relighting
  
• Thermocouple replacement
  
• Gas valve repairs
  
• Furnace maintenance
  
• Full system replacements
  
• Same-day heating service in Cupertino, CA
  

Call (408) 740-7079 or visit www.hvaccupertino.com for fast, reliable furnace repair.