Airtemp Furnace Flame Sensor Guide: Testing, Troubleshooting, and Replacement

The Airtemp furnace flame sensor is a small but critical safety component that confirms a gas burner is lit. This guide explains how the sensor works, common failure signs, testing and replacement steps, compatibility considerations, and maintenance tips to keep an Airtemp furnace running safely and efficiently. Technicians and homeowners will find actionable procedures, cost estimates, and safety warnings relevant to U.S. residential systems.

Item	Typical Value
Sensor Type	Single probe thermocouple-like sensor
Typical Voltage	Microamps DC (generates small current)
Material	Stainless steel probe, ceramic/metal base
Replacement Cost	$10–$60 (part only)
Labor Estimate	$80–$200 in the U.S.

How An Airtemp Furnace Flame Sensor Works

The flame sensor in an Airtemp furnace is a safety device that detects whether the gas pilot or burners are producing a flame. It senses ionization or thermoelectric current when a flame is present and sends a small electrical signal to the control board. If the control board does not receive this signal within a set period after ignition, it shuts down the gas valve to prevent unburned fuel buildup.

Key Point: The flame sensor does not ignite the furnace; it only confirms flame presence and prevents gas flow if flame is absent.

Common Signs Of A Failing Flame Sensor

Recognizing sensor failure early can prevent repeated furnace lockouts and unsafe conditions. Common symptoms include: frequent ignition cycles followed by shutdown, furnace running for a short time then going into fault, visible corrosion or build-up on the sensor probe, and error codes related to flame detection on the furnace control board.

• Repeated Lockouts: Furnace lights, then shuts off shortly after.
• Intermittent Operation: Works sometimes, fails at other times, often related to temperature or vibration.
• Visible Wear: Carbon, soot, or rust on the sensor probe reduces sensitivity.
• Error Codes: Control board or thermostat may indicate “no flame sensed” code.

Types And Compatibility For Airtemp Systems

Airtemp furnaces use industry-standard flame sensor designs, typically a single straight probe mounted in front of the burner flame path. Replacement sensors for Airtemp are often interchangeable with other makes, but differences in mounting brackets, probe length, and connector type require checking specifications.

Compatibility Checklist: Probe length, mounting style, electrical connector, and sensor orientation must match the original to ensure reliable flame detection.

Tools And Safety Precautions Before Starting

Working on gas furnaces requires caution. Before testing or replacing an Airtemp furnace flame sensor, disconnect power to the furnace at the breaker and shut off the gas supply if any gas-line work is needed. Allow the furnace to cool to avoid burns.

Recommended tools include: multimeter capable of microamp DC readings, nut drivers or screwdrivers to remove the access panel, fine-grit sandpaper or emery cloth, replacement sensor, and safety gloves and goggles.

How To Test An Airtemp Furnace Flame Sensor

Testing the flame sensor can determine whether cleaning will restore function or a replacement is needed. The most reliable test measures the microamp signal when the burner is lit. A simpler functional check compares behaviour before and after cleaning.

1. Turn Off Power: Shut off furnace power at the breaker and remove the access panel.
2. Locate Sensor: The sensor is a thin metal rod positioned in the flame path above the burners.
3. Inspect Probe: Look for soot, oxidation, or bending in the probe; note mounting and connector wiring.
4. Reapply Power And Light Furnace: With the panel temporarily open and power restored, allow the furnace to go through an ignition cycle.
5. Measure Signal: Use a microamp-capable multimeter; place the meter leads between the sensor terminal and ground. Typical readings when flame is present are in the range of 2–10 microamps depending on system design.
6. Interpret Results: Low or zero microamps with confirmed flame indicates a failing sensor or wiring issue.

Important: Multimeter tests may require a technician level of experience; inaccurate connection or measurement can cause erroneous readings.

Cleaning Vs. Replacing The Flame Sensor

In many cases, the sensor probe becomes coated with scale, soot, or oxidation that prevents proper flame sensing. Cleaning the probe is often an effective first step and is a common part of routine furnace maintenance.

Cleaning Steps: Power off the furnace, remove the sensor, gently clean the probe with fine-grit sandpaper or emery cloth until shiny, wipe with a clean cloth, and reinstall. Avoid aggressive scraping or chemicals that can damage the probe surface.

When To Replace: Replacement is recommended if cleaning does not restore proper microamp readings, the probe is bent or physically damaged, or the sensor repeatedly fails within a short period after cleaning.

Step-By-Step Replacement Procedure

Replacing an Airtemp furnace flame sensor is straightforward for those comfortable with basic HVAC tasks. The following steps describe a typical replacement procedure.

1. Power Off: Disconnect electrical power to the furnace at the breaker.
2. Access Burner Compartment: Remove the furnace access panel using appropriate tools.
3. Locate And Remove Sensor: Unplug the sensor’s wire connector and remove the mounting screw or clip holding the sensor in place.
4. Note Orientation: Observe sensor probe position and mounting to ensure correct reinstallation.
5. Install New Sensor: Insert the replacement sensor into the mounting slot, secure it with screw or clip, and reconnect the wire lead.
6. Restore Power And Test: Replace the panel, restore power, cycle the furnace and monitor for normal ignition and sustained operation.

Tip: Keep the replacement sensor probe positioned so it receives consistent flame contact; incorrect placement can trigger false lockouts.

Diagnostic Wiring And Control Board Considerations

Sometimes the problem lies with the wiring harness or the furnace control board rather than the flame sensor itself. Corroded connectors, broken wires, or a defective board can prevent flame current from reaching the sensing circuit.

When Testing Wiring: Check for continuity and secure connections. Look for burnt or melted insulation that indicates a prior fault. If wiring is intact and sensor readings are still low, a control board fault may be suspected and professional diagnosis is recommended.

Costs And Time Estimates

Replacement parts for Airtemp flame sensors are relatively inexpensive. A direct replacement sensor typically costs between $10 and $60 depending on OEM or aftermarket options. Professional service adds labor, with common U.S. rates placing total costs in the $100–$300 range for diagnosis and replacement.

Homeowners with mechanical aptitude can often replace the part in 20–40 minutes, while thorough diagnosis by an HVAC technician may take 60–90 minutes.

Maintenance Tips To Prevent Future Failures

Regular maintenance can extend sensor life and reduce service calls. Recommended practices include annual furnace tune-ups, cleaning the flame sensor during maintenance visits, replacing air filters on schedule, and ensuring burners are properly adjusted to reduce soot.

• Schedule Annual Tune-Ups With A Qualified Technician.
• Clean Or Replace The Flame Sensor When Performing Routine Maintenance.
• Maintain Proper Ventilation And Air Flow To Prevent Soot Build-Up.
• Use High-Efficiency Filters To Reduce Particulate Buildup In The Combustion Area.

Safety And Regulatory Notes

Working on gas appliances involves safety and legal considerations. Many jurisdictions require licensed HVAC technicians to perform gas valve, burner, or control board repairs. Homeowners should consult local codes before attempting gas-related repairs and always follow manufacturer instructions in the Airtemp furnace manual.

Safety Reminders: Always cut power before accessing internal components, avoid modifying gas lines without a licensed professional, and ensure proper combustion and venting after any service to prevent carbon monoxide hazards.

Troubleshooting Checklist For Technicians And DIYers

The following checklist helps narrow down causes of flame-sensing problems in Airtemp furnaces.

1. Visual Inspection: Check probe condition, wiring, and mounting orientation.
2. Clean Sensor: Remove oxidation and soot from the probe.
3. Functional Test: Observe ignition and shutdown behavior after cleaning.
4. Microamp Measurement: Measure flame sensor current during burner operation.
5. Wiring Check: Test continuity and inspect connectors for corrosion.
6. Control Board: Review error codes and check board for faults or damage.
7. Replace Sensor: If tests indicate low signal or physical damage.

Frequently Asked Questions About Airtemp Flame Sensors

How Long Does A Flame Sensor Last?

With regular maintenance, a flame sensor can last many years. Frequent cycling, dirty burners, or corrosive environments can shorten life expectancy. Replacement is inexpensive compared to other furnace components.

Can A Flame Sensor Be Cleaned Instead Of Replaced?

Yes, cleaning is the first recommended step. Many intermittent sensing problems are resolved by careful cleaning. If issues persist after cleaning, replacement is advisable.

Is It Safe For A Homeowner To Replace The Flame Sensor?

Homeowners comfortable with basic electrical isolation and component replacement can often safely replace the sensor. However, any work involving gas valves, burners, or control board diagnostics is best handled by a licensed HVAC technician.

Will Replacing The Flame Sensor Fix All Ignition Problems?

Not always. Ignition problems can stem from faulty igniters, gas valves, control boards, safety switches, or wiring. The flame sensor addresses flame detection issues specifically.

Where To Buy Replacement Sensors And OEM Tips

Replacement Airtemp flame sensors are available through HVAC parts suppliers, online marketplaces, and some big-box retailers. For best results, match the part number from the original sensor or consult the Airtemp furnace manual for approved replacements.

OEM Advice: Using OEM or high-quality aftermarket parts and retaining original sensor orientation and mounting improves long-term reliability.

Additional Resources And References

For complex diagnosis consult Airtemp technical documentation, HVAC service manuals, or contact authorized service providers. Online forums and manufacturer support pages can provide model-specific guidance but verify any advice against official documentation.

Key resources include the Airtemp furnace installation and service manual, National Fuel Gas Code for safety standards, and training materials from recognized HVAC education providers.

Resource	Use
Airtemp Service Manual	Model-specific wiring diagrams and part numbers
NFPA/National Fuel Gas Code	Gas appliance safety and installation standards
HVAC Training Centers	Technical training for advanced diagnostics

If further assistance is required, contacting a licensed HVAC technician or an authorized Airtemp service center is recommended for safe, code-compliant repairs and diagnostics.