Concord Furnace Flame Sensor: Troubleshooting, Replacement, and Maintenance

The Concord furnace flame sensor is a small but essential component that confirms combustion and keeps modern gas furnaces running safely. This article explains how Concord flame sensors work, common symptoms of failure, step-by-step testing and replacement guidance, maintenance tips, compatibility notes, cost expectations, and when to call a professional.

Item	Typical Value
Sensor Type	Thermocouple / Metal Rod Ionization Sensor
Common Location	Immediately in front of the furnace burner assembly
Average Replacement Cost	$25–$120 For Parts, $100–$300 Installed
Expected Lifespan	5–15 Years With Regular Maintenance

What Is A Concord Furnace Flame Sensor And Why It Matters

A Concord furnace flame sensor is a safety device that detects whether a gas burner has successfully ignited. If the sensor does not detect flame, it signals the control board to shut off the gas valve to prevent raw gas from accumulating. This function is critical for safety and efficient furnace operation.

How The Flame Sensor Works

Most Concord furnaces use an ionization-type flame sensor, a thin metal rod positioned so the flame touches it when burners ignite. The sensor generates a microamp electrical signal when the flame is present. The furnace control board monitors that signal and allows the system to continue normal cycling as long as the current is within expected range.

Key Functional Points

• Ionization Principle: Flame creates a conductive path that lets a tiny current flow through the sensor.
• Control Board Interaction: Detects the current and either sustains the gas valve or triggers a safety shutdown.
• Sensitivity: The sensor reads in microamps; dirt, corrosion, or misalignment can reduce signal below detection thresholds.

Common Symptoms Of A Failing Concord Flame Sensor

Recognizing signs of a failing flame sensor helps prevent repeated lockouts and unsafe conditions. Typical symptoms include frequent furnace short-cycling, ignition followed by immediate shutdown, error codes or blinking lights indicating flame failure, and the furnace requiring multiple restart attempts to stay lit.

Other Indicators

• Yellow or irregular burner flame instead of a steady blue flame.
• Visible buildup of soot or corrosion on the sensor rod.
• Intermittent operation that sometimes resolves after cooling down or tapping the furnace cabinet.

Before You Start: Safety And Preparation

Working on a gas furnace involves safety risks. Turn off power at the furnace switch and the circuit breaker and shut off the gas supply before inspecting or replacing the flame sensor. Wear safety gloves and eye protection. If unsure about gas valve work or any wiring, call a licensed HVAC technician.

How To Test A Concord Furnace Flame Sensor

Testing can confirm whether the sensor is the root cause. Basic testing includes visual inspection, cleaning, and measuring microamp output with a multimeter. Follow these steps in order to diagnose the sensor.

Step-By-Step Visual Inspection

1. Turn off power and gas to the furnace.
2. Remove the furnace access panel to locate the sensor—typically a thin metal rod mounted near the burners with a single wire lead.
3. Check for visible buildup, soot, or bending; ensure the sensor tip is properly positioned in the flame path.

Cleaning Procedure

1. If dirty, remove the sensor mounting screw and gently pull the sensor from its bracket.
2. Use a fine abrasive pad or emery cloth to remove light buildup—avoid heavy scraping that could damage the rod.
3. Wipe with a clean, lint-free cloth and re-install, ensuring proper alignment with the flame.

Electrical Testing With A Multimeter

1. After reinstalling, restore power and gas. Start a heating cycle so the burners light.
2. Set a multimeter to the microamp range if available. Connect the meter between the sensor lead and ground following manufacturer instructions.
3. A healthy flame sensor typically reads between 2 to 10 microamps depending on furnace model. Readings significantly below this range indicate a weak or failing sensor.

Replacement Guide For A Concord Furnace Flame Sensor

If cleaning does not restore proper operation or microamp readings remain low, replacement is usually the most effective solution. Most Concord flame sensors are inexpensive and straightforward to replace.

Tools And Parts Needed

• Replacement Concord-compatible flame sensor (OEM part number if available).
• Screwdriver or nut driver, fine emery cloth, multimeter, safety gloves.

Step-By-Step Replacement

1. Turn off power and gas to the furnace.
2. Remove the access panel and locate the sensor; note orientation and connection point for the wire.
3. Disconnect the wire and remove the mounting screw. Carefully pull out the old sensor.
4. Install the new sensor in the same orientation; tighten the mounting screw snugly but not over-tightened.
5. Reconnect the wire, restore power and gas, and initiate a heat cycle to confirm proper operation. Verify the furnace no longer locks out and that the sensor reads healthy microamps if tested.

Compatibility And Choosing The Right Sensor

Concord furnace models may use different sensors; using the correct OEM sensor or an approved aftermarket equivalent ensures fit, correct sensing length, and reliable signal. Check the furnace model number and cross-reference with part lists or the Concord parts catalog.

Tips For Buying

• Match Length And Mounting Style: Sensor rod length and mounting flange must match to sit correctly in the flame.
• Confirm Electrical Connector Type: Some sensors use spade terminals, others ring terminals.
• Prefer OEM Or Reputable Brands: Ensures consistent microamp output and durability.

Maintenance Tips To Extend Flame Sensor Life

Regular maintenance reduces flame sensor failure and improves furnace reliability. Scheduled cleaning during seasonal tune-ups is the most effective preventive step.

Practical Maintenance Steps

• Inspect and clean the flame sensor annually or during every preventive maintenance visit.
• Keep burners and combustion chamber clean—soot and debris accelerate sensor degradation.
• Maintain proper combustion by ensuring correct air-fuel mixture and regular burner adjustments by a technician.

Cost Expectations And Labor Considerations

Replacement parts for Concord flame sensors usually range from $25 to $120 depending on OEM status and model specificity. If hiring a technician, total costs typically range from $100 to $300, factoring in diagnostic time and service call fees.

When Replacement Is More Economical

• If the furnace is older and other components show wear, a comprehensive service or component upgrades might be more cost-effective.
• Repeated sensor failures often indicate underlying issues such as poor combustion, faulty control board, or wiring problems that require professional diagnosis.

Troubleshooting Related Components

When flame sensor issues persist after replacement, examine related components. Faulty gas valves, ignition controls, burner alignment, and control board logic can mimic sensor failures. Wiring connectors and grounding problems can also prevent proper detection.

What To Check Next

• Inspect wiring for corrosion, loose connectors, or damaged insulation.
• Verify ground connections and chassis bonding—poor grounding can reduce microamp signal.
• Confirm that the ignitor and burners produce a stable flame shape that contacts the sensor rod.

When To Call A Professional

A homeowner can handle inspection and simple replacement, but call a licensed HVAC technician if there is any uncertainty about gas handling, wiring, or repeated failures. Professionals will safely diagnose control boards, gas valves, and combustion quality and can perform calibrated microamp testing and repairs.

Frequently Asked Questions About Concord Furnace Flame Sensors

How Often Should A Flame Sensor Be Replaced?

Flame sensors can last 5–15 years depending on operating conditions and maintenance. Annual inspection and cleaning often extend service life and delay replacement.

Can A Dirty Flame Sensor Cause Carbon Monoxide Issues?

A dirty sensor alone does not cause carbon monoxide, but it can allow unsafe combustion patterns to go undetected. Proper burner maintenance reduces risk of incomplete combustion and CO generation.

Is It Safe To Tap The Sensor To Get The Furnace To Restart?

Tapping the sensor temporarily may mimic contact and restart the furnace but is not a safe permanent fix. It indicates a failing sensor or loose connection that requires repair or replacement.

Key Takeaways And Best Practices

Regular inspection and cleaning of the Concord furnace flame sensor is the most cost-effective way to maintain reliable furnace operation. When failures occur, follow safe diagnostic steps, test microamp output if possible, and replace the sensor with a compatible part. For persistent problems, engage a licensed HVAC professional to ensure gas safety and correct system operation.

Action	Recommendation
Annual Maintenance	Inspect and clean flame sensor, burners, and combustion area
Sensor Reading	Healthy: ~2–10 microamps (model-dependent)
Replacement	Use OEM or equivalent matched by length and connector
Professional Help	Call for repeated lockouts, gas valve or control board issues

If more model-specific guidance is needed, provide the Concord furnace model number and current symptoms for targeted troubleshooting and parts recommendations.