The furnace flame keeps going out, leaving a home cold and a homeowner frustrated. This article explains why a furnace flame goes out, how to safely diagnose common problems such as pilot light or intermittent burners, and practical steps to fix or prevent reoccurrence. Clear troubleshooting steps and guidance on when to call a professional are included for U.S. homeowners.
| Symptom | Likely Causes | Immediate Action |
|---|---|---|
| Pilot Light Keeps Going Out | Thermocouple Failure, Drafts, Dirt | Relight Pilot, Clean, Replace Thermocouple |
| Burner Flames Go Out During Operation | Faulty Flame Sensor, Clogged Air Intake, Gas Pressure Issues | Inspect Flame Sensor, Clean Vents, Check Gas Supply |
| Intermittent Flame | Control Board, Limit Switch, Venting Blockage | Reset, Inspect Vents, Call Technician |
Content Navigation
- How Furnace Flames Work
- Common Reasons The Furnace Flame Keeps Going Out
- Safety Considerations Before Troubleshooting
- Step-By-Step Troubleshooting Guide
- DIY Fixes That Often Work
- When To Call A Professional
- Common Parts That May Need Replacement
- Preventive Maintenance To Avoid Future Flame Outages
- How Weather And Home Changes Affect Flame Stability
- Cost Considerations And Budgeting
- Frequently Asked Questions
- Resources And Where To Get Help
How Furnace Flames Work
A gas furnace uses a gas valve, ignition system (pilot or electronic igniter), burners, and a safety flame detection device such as a thermocouple or flame sensor to maintain combustion. When the thermostat calls for heat, the system opens the gas valve and initiates ignition. The flame detection device confirms presence of flame and keeps the gas valve open. If detection fails, the valve closes and the furnace flame goes out to prevent unburned gas buildup.
Common Reasons The Furnace Flame Keeps Going Out
Faulty Thermocouple Or Flame Sensor
The most common reason a standing pilot keeps going out is a failing thermocouple; in modern furnace systems the flame sensor performs the same safety function. When the sensor or thermocouple becomes dirty or worn, it can fail to register flame and will shut off the gas supply.
Dirty Or Misaligned Pilot Or Burner
Accumulated soot, spider webs, or dust on the pilot or burners can interrupt proper ignition or flame stability. Cleaning or realigning the pilot flame often restores reliable operation.
Poor Venting Or Drafts
Negative pressure, backdrafts, or a blocked chimney can blow out the pilot or burner flame. Changes in wind or HVAC fan operation may cause intermittent outages. Inspecting and securing venting is essential for flame stability and safety.
Gas Supply Problems
Low gas pressure, a partially closed gas valve, or issues from the utility provider can cause the flame to go out. If multiple gas appliances are affected, suspect supply or regulator problems. Never attempt complex gas repairs; this requires a licensed technician.
Faulty Ignition Control Or Limit Switches
Modern furnaces use electronic ignition and control boards. A failing control board, relay, or high-limit safety switch can interrupt ignition or shut burners off mid-cycle. Electronic faults often require diagnostic tools and replacement parts.
Safety Considerations Before Troubleshooting
Turn off gas and power when performing any inspection beyond simple pilot relight procedures. If a gas smell is present, evacuate the home and call the gas company immediately. Carbon monoxide and gas leaks are life-threatening; install a CO detector near sleeping areas and test regularly.
Step-By-Step Troubleshooting Guide
1. Check Thermostat And Power
Confirm the thermostat is set to heat and the temperature is above the current room temperature. Verify the furnace has power: check circuit breakers and the furnace switch near the unit. Simple electrical issues are common and easy to resolve.
2. Inspect Pilot Light (Standing Pilot Systems)
If the pilot light keeps going out, attempt to relight following the manufacturer’s instructions. Observe the pilot flame: it should be steady and blue. A yellow or weak flame suggests dirt or gas pressure problems. Relight only if comfortable and the area is free of odors.
3. Clean The Flame Sensor Or Thermocouple
For electronic ignition systems, remove the flame sensor and gently clean with fine emery cloth to remove film and build-up. For thermocouples, clean the tip and ensure proper positioning in the pilot flame. Regular cleaning improves detection reliability.
4. Check Air Intake And Venting
Inspect intake vents, exhaust flues, and chimneys for blockages, bird nests, or debris. Ensure exterior vents are not obstructed by snow or leaves. Proper airflow prevents backdrafts and keeps flames stable.
5. Examine Gas Supply And Valves
Confirm gas to the furnace is fully open at the shutoff valve and other appliances are receiving gas. If low pressure is suspected, contact the gas utility or a licensed technician. Never attempt to modify gas valves beyond fully open/close actions.
6. Observe For Error Codes
Many furnaces flash LED codes that indicate specific faults such as flame failure or limit trips. Refer to the furnace manual to decode lights and follow recommended diagnostics. Codes save time and point to exact subsystems.
DIY Fixes That Often Work
- Clean Flame Sensor/Thermocouple: Remove and polish the tip gently, then reassemble.
- Clear Debris From Burners and Pilot: Use compressed air or a soft brush to remove dust and webs.
- Relight Pilot Correctly: Follow unit instructions and confirm a stable blue flame that envelops the thermocouple.
- Reset Furnace: Turn power off for 30 seconds and restore to reboot control boards and gas valves.
When To Call A Professional
If cleaning or basic checks do not resolve the issue, or if flame outages coincide with gas smells, frequent cycling, or error codes that point to gas valve or control board faults, contact a licensed HVAC technician. Technicians have tools to test gas pressure, inspect control boards, and safely replace components.
Common Parts That May Need Replacement
| Part | Symptoms Of Failure | Typical Replacement Cost Range |
|---|---|---|
| Thermocouple/Flame Sensor | Pilot/burners go out; intermittent ignition | $50–$200 Including Labor |
| Igniter Or Pilot Assembly | Ignition click but no flame | $100–$400 |
| Gas Valve | No gas flow; complete shutdown | $200–$700 |
| Control Board | Error codes; random shutdowns | $150–$800 |
Preventive Maintenance To Avoid Future Flame Outages
Schedule annual professional furnace tune-ups before winter to check gas pressure, clean burners, test safety devices, and inspect venting. Replace air filters every 1–3 months to ensure proper airflow. Routine maintenance reduces flame outages and extends furnace life.
How Weather And Home Changes Affect Flame Stability
High winds, negative pressure from exhaust fans, or recent home sealing improvements can create drafts or pressure imbalances that extinguish flames. Examine HVAC fan settings and consider adding make-up air or drafting solutions if negative pressure is suspected. Understanding home airflow can solve intermittent flame problems.
Cost Considerations And Budgeting
Minor repairs like cleaning or replacing a flame sensor are low-cost, often under $200. Major components like gas valves or control boards can reach several hundred dollars plus labor. Consider replacement if the furnace is older than 15–20 years and repair costs approach replacement value. Obtain multiple estimates from licensed contractors for larger repairs.
Frequently Asked Questions
Why Does The Pilot Light Keep Going Out Only When It’s Windy?
Wind or drafts can disturb the pilot flame or create negative pressure in flues. Inspect external vents for obstructions and ensure the pilot shield and pilot tube are properly positioned. Addressing external drafts typically resolves weather-related outages.
Is It Safe To Relight The Pilot Myself?
Relighting is safe when following manufacturer instructions and when no gas odor exists. If a gas smell is present, leave immediately and call the gas company. When in doubt, contact a pro.
Can A Dirty Filter Cause The Furnace Flame To Go Out?
A clogged filter reduces airflow, which can trigger high-limit switches and shut the burners off. Replace filters regularly to maintain steady combustion and prevent safety trips. Filter maintenance is a simple preventive measure.
Resources And Where To Get Help
Consult the furnace owner’s manual for model-specific instructions and error code tables. For gas supply issues or suspected leaks, contact the local utility provider. For repairs beyond basic cleaning or relighting, hire a licensed HVAC contractor or use resources from the Air Conditioning Contractors of America to find qualified technicians. Professional help ensures safe, code-compliant repairs.
If the furnace flame keeps going out despite basic troubleshooting, prioritized safety checks and timely professional diagnostics will restore reliable heating and reduce risk.
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Request at least three estimates before making your choice. You can click here to get three free quotes from local professionals. These quotes include available rebates and tax credits and automatically exclude unqualified contractors. - Negotiate Smartly
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