Does a Furnace Pilot Light Always Stay On

The pilot light behavior depends on the furnace type, ignition system and safety controls. This article explains why pilot lights go out, when they should stay lit, safety precautions and how modern furnaces use electronic ignition systems to eliminate standing pilots.

Question	Short Answer
Does a pilot light always stay on?	Not always — older furnaces typically keep it lit; many modern units do not.
Why does it go out?	Drafts, dirt, thermocouple failure, gas supply or safety shutoff.
Is it safe to relight?	Relight only if no gas smell and follow manufacturer instructions; call a professional for repeated outages.

What A Pilot Light Is And How It Works

A pilot light is a small, continuous flame used to ignite the main gas burners in older gas furnaces and appliances. It typically consists of a small gas jet and a flame that remains lit whenever the unit has a gas supply and the safety system permits it.

The pilot assembly includes a gas valve, pilot orifice and a thermocouple or thermopile sensor. The thermocouple senses the heat from the pilot and keeps the gas valve open, shutting off gas if the pilot goes out to prevent unburned gas from accumulating.

Types Of Furnace Ignition Systems

Standing Pilot (Constantly Lit)

Older furnaces often use a standing pilot that remains lit 24/7. This design is simple and reliable but wastes gas continually to keep the pilot flame burning.

Intermittent Pilot

Some systems use an intermittent pilot that lights when the thermostat calls for heat and stays lit for a limited period. This reduces fuel waste compared with a standing pilot.

Electronic Ignition And Hot Surface Igniters

Modern furnaces commonly use electronic ignition systems—either spark ignition or hot surface igniters—that light the burners only when needed. These systems eliminate the need for a continuously burning pilot.

Why A Pilot Light Might Go Out

Several factors can extinguish a pilot flame. Common causes include drafts, dirt and soot buildup, a weak or bent pilot flame, low gas pressure or issues with the thermocouple/thermopile.

Other causes are strong air currents near the venting, recent service or repairs that disturbed the pilot assembly, and insects or spider webs blocking the pilot orifice.

Signs The Pilot Light Is Out Or Failing

• If the furnace fails to start and there is no pilot flame, the pilot is likely out.
• A pilot that frequently flickers or is yellow instead of steady blue often indicates a problem.
• Gas odors near the furnace suggest a dangerous leak and require immediate action.

Is It Normal For A Pilot Light To Go Out Occasionally?

An occasional pilot outage can happen and is not always a sign of a major problem. Short interruptions in gas supply, brief drafts during storms, or accidental disturbance during cleaning can extinguish a pilot.

However, repeated or persistent outages indicate an underlying issue—such as a failing thermocouple, clogged pilot orifice, or venting problems—that deserves professional attention.

How To Safely Relight A Pilot Light

Always follow the furnace manufacturer’s instructions printed on the unit or in the manual. General safe steps include turning the gas control to “off” for several minutes, ensuring no gas smell, and then using the specified pilot lighting procedure.

If a gas odor is present, evacuate the home, avoid using electrical switches or phones inside, and call the gas utility or emergency services from a safe distance.

When To Stop Relighting And Call A Professional

If the pilot light goes out more than once, relighting does not hold, the flame appears weak or yellow, or there are any signs of a gas leak, the furnace should be serviced by a licensed technician.

Repeated outages can indicate faulty thermocouples, gas valve issues, venting blockages or combustion air problems, which require diagnostic tools and replacement parts that professionals provide.

Thermocouple And Thermopile: Safety Sensors Explained

The thermocouple is a low-voltage sensor that detects the pilot’s heat and signals the gas valve to remain open. A failing thermocouple often causes the pilot not to stay lit.

Thermopiles generate more millivolts and are used in systems with intermittent pilot or standing pilot that require slightly different control logic. Both components are common failure points in older systems.

Energy And Cost Considerations

Maintaining a standing pilot consumes additional gas—typically 20 to 70 therms per year depending on pilot size and local gas prices. Modern electronic ignition furnaces eliminate that continuous consumption and improve efficiency.

Replacing an old furnace with an electronically ignited model can lower fuel costs and reduce safety risks associated with a continuous pilot flame.

Safety Risks Associated With Pilot Lights

A standing pilot carries risks if the flame goes out while the gas valve remains open, which is why safety sensors like thermocouples are critical. Accumulated unburned gas can cause explosions or asphyxiation hazards.

Carbon monoxide (CO) is a concern when combustion is incomplete due to blocked vents, so regular inspections and proper venting are essential for safety.

Troubleshooting Steps For Homeowners

1. Check For Gas Odor: If present, evacuate and call professionals.
2. Inspect The Pilot Flame: A steady blue flame is healthy; yellow or flickering indicates a problem.
3. Clean The Pilot Area: With the gas off and power disconnected, gently remove dust and webs from the pilot area.
4. Check Drafts: Seal gaps or adjust venting that may blow out the flame.
5. Attempt Relight Per Instructions: Follow the furnace label; if it won’t stay lit, stop and call a technician.

Maintenance Practices To Keep A Pilot Light Reliable

Annual furnace service helps prevent pilot light problems. Technicians clean the pilot orifice, inspect the thermocouple/thermopile, check gas pressure, and verify venting and combustion efficiency.

Simple homeowner tasks like keeping the furnace area clear, replacing filters, and ensuring good combustion air can reduce pilot interruptions.

When Upgrading Makes Sense

Replacing a furnace may be more cost-effective than repeated repairs if the unit is old, inefficient or has recurring pilot issues. New furnaces with electronic ignition increase efficiency and reliability.

Homeowners should compare repair costs, furnace age, efficiency ratings and potential energy savings when deciding whether to upgrade.

Local Codes, Utilities And Rebates

Local building codes and utility programs may influence whether a standing pilot is acceptable or if conversion to electronic ignition is recommended. Some utilities offer rebates for high-efficiency furnace installations.

Consult local utility providers and licensed HVAC contractors for guidance on code compliance and available incentives.

Key Takeaways For Homeowners

• Pilot lights do not always stay on: Older units often keep them lit, modern furnaces usually do not.
• Intermittent outages may be normal; repeated failures are not.
• Safety sensors like thermocouples are designed to shut off gas if the pilot is out.
• Relight only when no gas smell is present and follow manufacturer instructions.
• Consider replacing an older furnace with electronic ignition to save fuel and improve safety.

Resources And Next Steps

For further information, consult the furnace manual, the National Fire Protection Association (NFPA), the U.S. Department of Energy guidance on furnace efficiency, and a licensed HVAC technician for inspections and repairs.

If the pilot light will not stay lit after basic troubleshooting, arrange a professional service call to diagnose thermocouple issues, gas valve faults, or venting problems to ensure safe operation.