Old Furnace Pilot Light Problems and Safe Solutions

The pilot light on an old furnace is a small but crucial component that ignites the burner to heat a home. When it goes out or flickers, the result can be no heat, frequent cycling, or safety concerns. This article explains why pilot lights fail, how to relight them safely, when to call a professional, and when replacing an old furnace may be the better option.

Symptom	Likely Cause	Quick Action
Pilot Won’t Stay Lit	Dirty pilot or faulty thermocouple	Clean pilot; test/replace thermocouple
Weak Or Yellow Flame	Blocked orifice; poor combustion	Clean orifice; inspect venting
Clicking Or Humming	Gas valve or control issues	Call HVAC technician

What Is A Pilot Light And How It Works

An old furnace pilot light is a continuously burning flame that ignites the main gas burner when the thermostat calls for heat. Pilot systems typically include a pilot assembly, a thermocouple or thermopile sensor, a gas valve, and the burner itself. The thermocouple detects heat from the pilot and keeps the gas valve open; if the pilot goes out, the thermocouple cools and shuts off the gas to prevent leaks.

Common Causes Of Pilot Light Problems

Pilot light issues in older furnaces often stem from age, dirt, or component wear. Understanding the most common causes can speed diagnosis and repair.

Drafts And Airflow Problems

Strong drafts, open windows, or poor venting can blow out the pilot or affect flame stability. Check for nearby drafts and ensure proper flue operation.

Dirty Pilot Or Orifice

Accumulated dust, soot, or spider webs can block the pilot orifice, weakening the flame or preventing ignition. Regular cleaning often restores proper flame strength.

Faulty Thermocouple Or Thermopile

A worn or misaligned thermocouple will fail to sense the pilot flame and shut the gas valve, causing repeated outages. Thermocouples are inexpensive but must be installed correctly.

Gas Supply Or Valve Problems

Low gas pressure, closed valves, or a failing gas control valve can prevent the pilot from lighting or staying lit. If the gas supply is interrupted, do not attempt extensive DIY repairs; contact a licensed technician.

Age And Component Wear

Older furnaces experience natural wear of ignition components and controls. Electronic controls, pilot assemblies, and gas valves may need replacement as part of routine maintenance.

How To Safely Relight An Old Furnace Pilot Light

If a pilot light goes out, relighting may be a straightforward safety task when done correctly. Always follow the furnace manufacturer’s instructions printed on the unit.

Preparation And Safety Checks

• Turn off the furnace and set the thermostat to off.
• Shut off the main gas supply or the furnace gas valve and wait five minutes to clear any residual gas.
• Ensure good ventilation and check for the smell of gas; if gas is present, evacuate the home and call the gas company.

Step-By-Step Relighting

1. Open the furnace access panel to locate the pilot assembly.
2. Turn the gas control knob to the “pilot” position and press/hold it while using a long match or built-in igniter.
3. Light the pilot and continue holding the control for 30–60 seconds to allow the thermocouple to heat.
4. Release the knob and verify the pilot stays lit; set the control back to “on.”
5. Replace the access panel and restore the thermostat setting.

If the pilot will not stay lit after several safe attempts, stop and call a professional.

When Not To Relight The Pilot Light

Relighting is not always appropriate. The following conditions require professional attention or caution.

• Persistent gas smell inside the home.
• Repeated pilot outages after relighting attempts.
• Visible corrosion, gas leaks at fittings, or damaged gas lines.
• Unusual noises, loud hissing, or pilot flame irregularities indicating a gas valve or regulator issue.

Maintaining An Old Furnace Pilot Light

Regular maintenance reduces pilot light failures and improves furnace efficiency. A few preventive steps can extend component life and reduce emergency calls.

Routine Cleaning

Cleaning the pilot orifice and nearby components annually removes soot and insect debris. Turn off gas and power before cleaning and use a soft brush or compressed air.

Check And Replace Thermocouples

Thermocouples commonly fail in older furnaces. Testing with a multimeter can confirm output; replacement is inexpensive and often restores reliable operation.

Inspect Venting And Flues

Blocked or corroded flues cause combustion issues and carbon monoxide risks. Ensure flues are clear and that the draft inducer or chimney functions correctly.

Annual Professional Tune-Up

An HVAC technician should perform annual inspections, clean burners, test gas pressure, and evaluate safety controls. Professional service catches problems that simple homeowner checks may miss.

When To Replace An Old Furnace Instead Of Repairing The Pilot

Repairing a pilot light makes sense when problems stem from accessible components. Replacement becomes preferable under several conditions.

• Frequent failures and escalating repair costs for aging parts.
• Furnace efficiency below current standards or unsafe combustion leading to carbon monoxide concerns.
• Unavailable replacement parts for very old models.
• Desire for modern features: electronic ignition, higher AFUE ratings, or compatibility with smart thermostats.

Electronic ignition systems eliminate a continuously burning pilot, improving efficiency and reducing standby gas use.

Cost Considerations: Repair Vs. Replacement

Repairing a pilot-related issue such as replacing a thermocouple typically ranges from low to moderate cost depending on labor and parts. Full furnace replacement is a larger investment but yields long-term savings.

Service	Typical Cost Range (US)
Thermocouple Replacement	$75 – $250
Pilot Orifice Cleaning	$50 – $150
Gas Valve Replacement	$300 – $900
Furnace Replacement	$2,500 – $8,000+

Costs vary by region, furnace brand, and access complexity. When repairs approach 50% of replacement cost, replacement often offers better value.

Safety Tips And Carbon Monoxide Awareness

Pilot light issues can create safety hazards if combustion is incomplete or venting is compromised. Proper precautions help protect occupants.

• Install and test carbon monoxide (CO) detectors on each level of the home.
• Never ignore a persistent gas odor; evacuate and call the gas company or 911.
• Keep the area near the furnace clear of flammable materials and stored items.
• Ensure professional inspection before operating an older furnace after prolonged dormancy.

Troubleshooting Checklist For Old Furnace Pilot Light Problems

Homeowners can run a simple checklist to gather information before calling a technician. This speeds diagnosis and helps determine urgency.

• Was the pilot lit and then went out, or will it not light at all?
• Is there a strong gas smell after turning the gas on?
• Is the pilot flame steady and blue, or weak and yellow?
• Has the furnace been serviced within the last 12 months?
• Are there signs of soot, corrosion, or insect nests near the pilot assembly?

Frequently Asked Questions About Old Furnace Pilot Lights

Why Does The Pilot Light Keep Going Out?

The most common reasons include a failing thermocouple, drafts, or a dirty pilot orifice. Cleaning and replacing worn components usually fixes the issue.

Can A Homeowner Replace A Thermocouple?

Yes, a homeowner with basic tools can replace a thermocouple, but proper alignment and connection are important. When in doubt, a licensed HVAC technician ensures safe and correct installation.

Is It Safe To Leave An Old Pilot Light On All The Time?

Older furnaces with pilot lights burn a small, continuous amount of gas, which is normal but less efficient than modern electronic ignition systems. Proper maintenance and venting are necessary for safety.

How Often Should A Pilot Assembly Be Serviced?

Annual inspection and cleaning are recommended, especially for older systems. More frequent checks may be necessary in dusty environments or homes with pests.

Resources And When To Call A Professional

If pilot light problems persist after basic troubleshooting, or if there are safety concerns, contact a licensed HVAC contractor. For gas leaks, contact the gas utility immediately and evacuate if necessary.

Useful resources include the furnace manufacturer’s manual, local utility safety guides, and the U.S. Consumer Product Safety Commission for carbon monoxide information.

Addressing pilot light problems promptly maintains comfort, reduces safety risks, and helps determine whether a repair or replacement provides the best long-term value.