Troubleshooting and Resetting Carrier Furnace Ignition Lockout Issues

Carrier Furnace Ignition Lockout – What to Do


Facing a furnace malfunction, especially during frigid weather, can be a major concern. Ignition lockout in a Carrier furnace can lead to heating disruption. Understanding the causes and troubleshooting steps is crucial. In this article, we explore common components, reasons behind ignition lockouts, and steps to reset your Carrier furnace.

Components to Inspect:

When dealing with a Carrier furnace ignition lockout, inspect the following components for potential issues:

1. Ignitor
2. Air filter
3. Fan
4. Limit switch
5. Flame detector

Understanding Ignition Lockout:

Ignition lockouts in Carrier furnaces are categorized as soft locks and hard locks. These lockouts aim to cut off power to the furnace in response to abnormal conditions detected by specialized sensors. Soft locks can be restarted, while hard locks render the furnace inoperable for three hours after four consecutive failed startup attempts.

Causes of Ignition Lockout:

Several factors can trigger ignition lockouts in Carrier furnaces. Understanding these causes is crucial for effective troubleshooting:

1. Flame Sensor Failure: A malfunctioning flame sensor, responsible for detecting the presence of a flame before igniting the furnace, can lead to ignition lockout. Regularly check and replace a damaged flame sensor.

2. Faulty Ignition System: A defective igniter can prevent the furnace from igniting. Replace a faulty igniter promptly to ensure proper operation.

3. Limit Switch Issues: The limit switch monitors air pressure and heat transfer temperature. If it fails to regulate pressure and temperature correctly, the system can lock out. Replacement is necessary to resolve this issue.

Common Causes for Limit Switch Trips:

Several issues, including component defects and external factors, can trip the limit switch and cause ignition lockout:

1. Clogged Air Filter: A dirty air filter reduces airflow, impacting the limit switch’s operation. Regularly replace air filters every 30-60 days to prevent this issue.

2. Leaking Air Duct: Sealing air ducts is crucial for maintaining proper pressure and heat flow, preventing the limit switch from tripping.

Determining Faulty Limit Switch:

Use a digital multimeter to assess the limit switch’s functionality. A voltage drop reading of 0.2 VDC or higher indicates a potential defect, requiring replacement.

Resetting a Carrier Furnace:

To reset your Carrier furnace, follow these steps:

1. Ensure the thermostat is turned off.
2. Turn off the circuit breaker or unplug the power cord.
3. Wait for 30 seconds.
4. Flip the circuit breaker back to the “on” position.
5. Adjust the thermostat to “on.”


Addressing ignition lockout issues in your Carrier furnace involves inspecting and maintaining critical components. Regular servicing and prompt replacement of faulty parts contribute to efficient furnace operation. If facing repeated ignition lockouts, consult with an HVAC technician for professional assistance. With the right knowledge and steps, you can troubleshoot and reset your Carrier furnace, ensuring uninterrupted heating during colder months.

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About the author


I am Ben , a seasoned HVAC specialist with over 6 of experience in the HVAC industry. I holds HVAC Certification and has a proven track record in providing expert advice on HVAC systems.