Goodman Furnace Flame Sensor Troubleshooting and Replacement

The flame sensor is a small but critical component that ensures safe operation of a Goodman furnace by confirming the burner flame is present. This article explains how the flame sensor works, common failure signs, step-by-step troubleshooting, safe replacement guidance, and maintenance tips to keep the furnace reliable and efficient.

Symptom	Likely Cause	Quick Fix
Furnace Starts Then Shuts Off	Dirty Or Faulty Flame Sensor	Clean Sensor Or Replace If Damaged
Frequent Lockouts	Poor Flame Detection Or Wiring Issue	Inspect Wiring, Clean Sensor, Check Flame Pattern
No Heat With Ignition Clicking	Sensor Not Sending Signal To Control Board	Test Sensor Continuity And Voltage

How A Goodman Furnace Flame Sensor Works

The flame sensor is a metal rod positioned in the path of the burner flame to detect ionization current produced by the flame. The furnace control board sends a small voltage to the sensor; when the flame ionizes the gas, a current flows through the sensor back to the control board, confirming combustion. If the control board does not see this current within a set timeframe, it shuts down the gas valve to prevent unburned gas buildup.

Common Symptoms Of A Bad Flame Sensor

Recognizing symptoms early prevents repeated lockouts and unnecessary part replacement. Common signs include repeated ignition cycles where the furnace lights then shuts off after a few seconds, the furnace going into a lockout state indicated by an LED error code, or no heat despite burners trying to ignite. Intermittent operation and visible soot or corrosion on the sensor are also indicators.

Typical Causes Of Flame Sensor Problems

Several factors lead to flame sensor failure. The most frequent cause is buildup of carbon, oil, or debris on the sensor rod which insulates it and prevents ionization current flow. Age and metal degradation, loose or corroded electrical connections, improper flame geometry, or problems with the control board and grounding issues can also cause failure.

Troubleshooting Steps Before Replacing The Sensor

Safety First

Always turn off power and gas to the furnace at the service switch and the breaker before inspecting internal components. Confirm power is off with a multimeter to avoid electric shock. If unsure, hire a qualified HVAC technician.

Visual Inspection

Inspect the flame sensor for visible carbon buildup, discoloration, or physical damage. Check the mounting bracket, wiring harness, and connector for corrosion or looseness. Examine the burner flame pattern—uneven or yellow flames can cause poor sensor detection.

Cleaning Procedure

Cleaning is the most cost-effective fix. Remove the sensor from its mounting using a nut driver or socket. Use a fine abrasive like 400–600 grit sandpaper or a gentle Scotch-Brite pad to remove carbon deposits. Wipe with a lint-free cloth dampened with isopropyl alcohol and allow to dry before reinstalling. Do not use coarse abrasives or emery cloths that can remove protective coating.

Electrical Testing

After cleaning and reinstalling, restore power and observe operation. If problems persist, test the sensor with a multimeter set to microamps if available; expected flame signal values often range from 2 to 10 microamps when the burner is lit. If the control board accepts readings, operation should be normal. An open circuit or zero reading indicates a defective sensor or wiring fault.

Control Board Check

If the sensor reads correctly but the furnace still locks out, inspect the furnace control board for error codes or damaged terminals. Check the ground connections and ensure the control board firmware and settings are compatible with the ignition system.

How To Replace A Goodman Furnace Flame Sensor

Parts And Tools Needed

• OEM-compatible Goodman flame sensor (match part number when possible)
• Nut driver or 7/16″ socket
• Screwdriver set
• Multimeter
• Isopropyl alcohol and lint-free cloth (for final cleaning)

Step-By-Step Replacement

1. Turn Off Power And Gas: Switch off furnace power at the breaker and the service switch; shut off the gas valve if performing major work.
2. Access The Burner Assembly: Remove the furnace access panel to reach the burners and flame sensor.
3. Disconnect Wiring: Carefully unplug the sensor lead from the connector on the control board or harness.
4. Remove The Sensor: Unscrew the mounting nut or bolt and gently slide the sensor from its bracket.
5. Install New Sensor: Position the new sensor in the same orientation and secure the mounting fastener snugly—avoid over-tightening.
6. Reconnect Wiring: Attach the electrical connector to the new sensor ensuring a clean, tight connection.
7. Restore Power And Test: Replace the access panel, turn on power and gas, and run the furnace through a heating cycle to verify proper ignition and continuous operation.

Note: The sensor must protrude into the flame at the same depth and angle as the original to ensure accurate detection.

When Cleaning Is Not Enough: Signs Replacement Is Required

Cleaning often restores function, but replacement is necessary if the sensor is physically bent, heavily corroded, shows pitting, or produces no microamp signal after testing. Recurrent failures may indicate alignment or burner problems that should be inspected by a technician. OEM replacement sensors are inexpensive and often the most reliable long-term solution.

Compatibility And Part Selection For Goodman Furnaces

Goodman furnaces use specific flame sensor lengths and mounting styles depending on the model series. Using the furnace model number found on the data plate helps ensure correct sensor selection. Aftermarket sensors are available but choosing an OEM or OEM-equivalent part reduces risk of fitment and performance issues.

Maintenance Tips To Extend Flame Sensor Life

• Schedule annual furnace tune-ups that include sensor inspection and burner cleaning.
• Replace air filters regularly to reduce dust and debris that can travel to the combustion chamber.
• Ensure proper combustion air supply and venting to maintain stable flame pattern.
• Address yellow or lifting flame issues promptly; they reduce sensor reliability.
• Keep the furnace area clean and free of contaminants that could be drawn into the burners.

Safety Considerations And When To Call A Professional

Working on furnaces involves gas, electricity, and combustion components that pose safety risks. If the flame sensor removal is obstructed by other components, or if diagnosing electrical or control board issues, a licensed HVAC technician should be engaged. A technician can also perform combustion analysis to ensure safe and efficient operation.

Cost Expectations And Warranty Notes

Flame sensors are typically low-cost parts, often ranging from $10 to $60 for OEM units. Labor costs for professional replacement vary by region and may be included in a furnace service call. Check the furnace warranty; some Goodman warranties cover certain components for specified periods and may influence repair decisions.

Preventing Future Lockouts And Improving Furnace Reliability

Regular maintenance and addressing signs early prevent repeated lockouts. Monitoring for intermittent operation, running the furnace through startup cycles after maintenance, and documenting any error codes help technicians diagnose recurring issues. Proper installation and timely replacement of the flame sensor reduce downtime and maintain heating comfort.

Useful Diagnostic Checklist

Check	Action
Visual Condition	Inspect For Carbon, Corrosion, Or Damage
Flame Pattern	Ensure Blue, Stable Flames Across Burner
Wiring And Connector	Verify Tight, Clean Connections And No Frayed Wires
Microamp Signal	Measure With Multimeter; Expect A Few Microamps
Control Board Errors	Check LED Codes Against Goodman Manual

Key Takeaways For Goodman Furnace Owners

Regular cleaning of the flame sensor often resolves ignition shutdowns, while accurate testing reveals electrical faults. OEM-compatible replacements are affordable and straightforward for those comfortable with basic furnace service tasks. For complex electrical or combustion issues, professional HVAC service ensures safe, effective resolution.

Readers seeking more model-specific guidance should reference the Goodman furnace manual or contact certified service professionals for tailored assistance.