Intertherm Furnace Pilot Light Troubleshooting and Repair

The Intertherm furnace pilot light plays a critical role in older gas heating systems. This article explains how the Intertherm furnace pilot light works, common reasons it goes out, safe relighting steps, diagnostics, repair options, and maintenance practices to keep a home heating system reliable and safe.

Symptom	Likely Cause	Quick Fix
Pilot won’t stay lit	Faulty thermocouple or dirty pilot assembly	Replace thermocouple; clean pilot orifice
No pilot flame	Gas supply or valve issue	Check gas supply; call technician
Weak pilot flame	Clogged orifice or low gas pressure	Clean orifice; inspect gas pressure
Intermittent shutdowns	Drafts, sensor faults, or control failures	Relocate pilot shield; test sensors

How The Intertherm Furnace Pilot Light Works

The pilot light is a small, continuous flame that ignites the main burners when the thermostat calls for heat. In many Intertherm furnace models the pilot is monitored by a thermocouple or thermopile that senses heat and keeps the gas valve open. If the pilot flame is absent or weak, the safety circuit closes the valve to prevent unburned gas from accumulating.

Key Components: pilot orifice, pilot tube, thermocouple/thermopile, gas valve, pilot shield. Understanding these parts helps pinpoint why a pilot light issue occurs.

Common Causes Of Pilot Light Problems

Pilot light issues often stem from a handful of recurring causes. Identifying the root cause reduces unnecessary replacements and helps prioritize safety.

• Dirty Orifice Or Pilot Tube: Soot, dust, or spider webbing can restrict gas flow and weaken or extinguish the flame.
• Worn Or Faulty Thermocouple/Thermopile: These sensors wear out or lose their ability to generate the millivolts needed to keep the gas valve open.
• Gas Supply Issues: Closed valves, interrupted service, or low gas pressure can prevent the pilot from lighting.
• Drafts Or Venting Problems: Strong drafts from nearby vents, open windows, or flue backdraft can blow out a pilot.
• Faulty Gas Valve Or Control Module: Mechanical failure in the gas valve or control board prevents ignition or stable pilot operation.
• Improper Pilot Flame Adjustment: If the flame is not centered on the thermocouple, the sensor won’t heat correctly.

Safety Precautions Before Troubleshooting

Working with gas and flame requires caution. Before attempting any inspection or relight procedure, follow safety steps to reduce risk.

• Turn off the furnace power at the switch and shut off the gas supply if instructed by the furnace manual.
• Ventilate the area if the smell of gas is present and avoid creating sparks or open flames.
• Do not proceed if there is a strong gas odor; evacuate and call the gas utility or a licensed technician.
• Use appropriate tools and long-handled lighters designed for pilot lighting to keep hands away from the flame.

How To Relight An Intertherm Furnace Pilot Light

Most Intertherm furnaces include specific relighting instructions on the furnace access panel. The following steps represent a general, safe method; consult the model’s manual for exact procedure details.

1. Turn the thermostat to OFF and switch the furnace power off.
2. Locate the pilot assembly and the gas control knob labeled OFF, PILOT, and ON.
3. Turn the gas control to OFF and wait five minutes to clear gas.
4. Turn the knob to PILOT, hold it depressed, and use the furnace’s pilot igniter button or a long lighter to light the pilot.
5. Keep the knob depressed for 30–60 seconds after the pilot lights to allow the thermocouple to heat.
6. Release the knob. If the pilot stays lit, turn the control to ON and restore power.
7. If the pilot does not stay lit after several attempts, stop and move to troubleshooting or call a technician.

Troubleshooting Steps If The Pilot Won’t Stay Lit

If the pilot either won’t light or won’t remain lit after relighting, perform these systematic checks to isolate the problem.

• Inspect The Pilot Flame Shape: A healthy flame should be steady and blue with a small yellow tip. Weak, flickering, or large yellow flames indicate problems.
• Clean The Pilot Orifice: Turn off gas and power, remove debris around the pilot opening, and use compressed air or a thin wire to clear the orifice carefully.
• Check Thermocouple Connection: Ensure the thermocouple nut at the gas valve is tight and the sensor is positioned in the flame.
• Test The Thermocouple: A multimeter can measure millivolts; a cold thermocouple should read near 0 mV, while a heated one may produce 25–30 mV. If readings are low, replace the thermocouple.
• Inspect For Drafts: Temporary shielding or adjusting venting can confirm if drafts are the cause.
• Verify Gas Supply: Confirm other gas appliances work, and check the furnace shutoff valve position.

When To Replace The Thermocouple Or Thermopile

Thermocouples and thermopiles are inexpensive parts that commonly fail after years of operation. Symptoms signaling replacement:

• Pilot lights but goes out when the knob is released.
• Insufficient millivolt output when heated.
• Visible corrosion, kinks, or breakage in the sensor lead.

Replacement is typically straightforward for someone comfortable with basic tools: disconnect the old sensor from the gas valve, remove the mounting clip, install the new sensor in the same position, and reconnect. If any doubt exists about gas connections, a licensed HVAC technician should perform the work.

Diagnosing Gas Valve And Control Problems

If the pilot and thermocouple test good, the gas valve or control module could be failing. Symptoms include clicking, no gas flow despite a hot thermocouple, or intermittent operation.

Testing a gas valve often requires specialized tools and knowledge. A technician can measure valve coil resistance and verify correct millivolt inputs and outputs. Replacing a gas valve can be more costly and typically warrants professional service for safety and to preserve warranty coverage.

Maintenance Tips To Prevent Pilot Light Issues

Regular maintenance reduces pilot light problems and improves furnace life and efficiency. Recommended actions:

• Schedule annual professional inspections and cleanings before the heating season.
• Clean the pilot assembly during yearly service or when soot accumulates.
• Keep the furnace area free of dust, debris, and pests to prevent orifice blockage.
• Check for drafts or changes in venting that could affect flame stability.
• Replace worn thermocouples proactively if the system shows intermittent signs of failure.

Parts, Costs, And Typical Repair Times

Common parts for pilot-related repairs are affordable, but labor and diagnosis add to total costs. Typical ranges in the U.S. market:

Part/Service	Typical Cost (Parts)	Typical Labor Time
Thermocouple	$10–$40	15–45 minutes
Pilot Orifice Cleaning	$0–$50 (if DIY or service call)	15–60 minutes
Gas Valve Replacement	$150–$600	1–3 hours
Control Module Replacement	$100–$400	1–2 hours

Costs vary by region, furnace age, and service provider. For safety-critical items like gas valves, professional installation is recommended.

When To Call A Licensed Technician

Certain signs indicate a need for professional service rather than DIY fixes. Contact a licensed HVAC technician if any of the following occur:

• Persistent gas smell or suspected leak.
• Pilot refuses to stay lit after cleaning and sensor replacement.
• Visible damage to the gas valve or control module.
• Complex issues such as venting problems, carbon monoxide alarms, or repeated shutdowns.

A qualified technician can perform gas leak testing, combustion analysis, and safe valve replacements that homeowners should not attempt without certification.

Frequently Asked Questions About Intertherm Furnace Pilot Lights

Why Does The Pilot Light Keep Going Out?

Common reasons include a failing thermocouple, blocked pilot orifice, drafts, or a weak gas supply. Identifying the specific symptom—no flame, weak flame, or flame that extinguishes—helps narrow the cause.

Can A Homeowner Replace The Thermocouple?

Yes, homeowners with basic mechanical skills can replace a thermocouple. Ensure the gas is off and follow manufacturer instructions. If the homeowner is uncertain about gas-tight connections, hire a professional.

Is It Worth Repairing An Old Intertherm Furnace?

Repair decisions depend on furnace age, efficiency, and condition. For furnaces older than 15–20 years with repeated failures, replacement with a modern high-efficiency system may offer better long-term value.

Can Pilot Issues Cause Carbon Monoxide Problems?

Pilot flame problems themselves rarely produce carbon monoxide, but venting issues, incomplete combustion, or cracked heat exchangers do. If carbon monoxide alarms sound or occupants feel ill, evacuate and call emergency services.

Resources And Further Reading

For model-specific instructions, consult the Intertherm furnace manual or the manufacturer’s support site. Local utility companies and licensed HVAC contractors provide safety guidance and professional inspection services.

Key Takeaway: Many pilot light issues are solvable through methodical cleaning, sensor testing, and safe relighting procedures, but safety and proper diagnosis take priority. When in doubt, a licensed HVAC professional ensures safe, code-compliant repairs.