Lennox SL22KLV Heat Pump Error Code 120: Thermistor Failure Detected

If your Lennox heat pump model SL22KLV is displaying error code 120, you’re likely dealing with a faulty thermistor that’s preventing proper ignition. Prompt action is necessary to avoid further damage.

You’ll need to diagnose the issue, potentially resetting the system or replacing the faulty thermistor, and inspect the ignition system for other potential failures. As you dig deeper into the problem, you’ll uncover more about the causes and symptoms of thermistor failure and learn how to prevent future errors.

Understanding Error Code 120

When your Lennox heat pump, including the SL22KLV model, displays error code 120, it’s a sign that the ignition system is malfunctioning.

This error code is often related to a faulty thermistor, which is a temperature-sensing device that helps regulate the ignition process.

If you’re experiencing error code 120, you must tackle the issue promptly to prevent further damage to your heat pump.

You may need to reset the system or replace the faulty thermistor, but in some cases, more extensive repairs or even replacement of the entire ignition module may be required.

Be sure to consult the user manual or contact a Lennox authorized technician to diagnose and repair error code 120, as it may require specialized knowledge and tools to resolve the issue.

Also, Read: Lennox SL22KLV Heat Pump Error Code 119: Outdoor Airflow Restriction Detected (Blocked Coil/Fan)

Causes of Thermistor Failure

Faulty wiring or corrosion on the thermistor’s electrical connections likely triggered the error code 120 on your Lennox heat pump.

This temperature sensor failure can also be caused by low refrigerant levels, which can affect the thermistor’s accuracy.

Dirty air filters can also contribute to thermistor failure by blocking airflow and causing the system to overheat.

A faulty control board can also trigger the error code, as it may not be able to read the thermistor’s signals correctly.

Crucial to address these potential causes to resolve the thermistor failure and get your heat pump running efficiently again.

Symptoms of a Faulty Thermistor

Your Lennox heat pump’s thermistor failure can exhibit several telltale signs.

When the thermistor fails, it can disrupt the heat pump’s ability to regulate temperature, leading to erratic performance.

• Inconsistent heating: Your heat pump is producing inconsistent heat, or it’s not heating at all.
• Error code 120: You may see an error code 120 on your heat pump’s display, indicating a thermistor failure.
• Unusual noises: You may hear unusual noises, such as clunking or rattling sounds, coming from the heat pump.
• Temperature fluctuations: You may notice temperature fluctuations in your home, even when the heat pump is running.

Also, Read: Lennox SL22KLV Heat Pump Error Code 118: Indoor Airflow Restriction Detected (Clogged Filter/Blocked Duct)

Diagnosing the Ignition System Problem

You’ll need to perform an Ignition System Check to identify the root cause of the error code 120, which could be related to Thermistor Failure Causes.

Check the ignition system for any signs of malfunction or failure, such as faulty spark modules or ignition coils.

Ignition System Check

As the ignition system is responsible for generating the high voltage needed to create sparks, this is vital to inspect the ignition coil, spark plug wires, and spark plugs themselves to identify the root cause of the Lennox heat pump’s error code 120.

When you’re checking the ignition system, make sure to:

• Verify the ignition coil’s resistance and voltage output to confirm it’s functioning within the specified range.
• Inspect the spark plug wires for signs of wear, damage, or corrosion that could be causing a communication error.
• Check the spark plugs for fouling or wear, which could be affecting the heating performance and leading to the error code 120.
• Confirm the gas valve is functioning properly, as a faulty valve could prevent the ignition system from generating the necessary sparks.

Thermistor Failure Causes

Faulty thermistor readings can trigger the Lennox heat pump’s error code 120, indicating a problem with the ignition system.

As you diagnose the issue, you’ll find that a faulty thermistor is a common cause of thermistor failure. This temperature-sensing device monitors the heat pump’s operating temperature, and a malfunction can prevent the heat pump from functioning properly.

Check the thermistor’s resistance values against the manufacturer’s specifications to identify the problem. Additionally, a short circuit or open circuit in the thermistor wiring can also cause the error code, which can be diagnosed by performing a continuity test on the wiring and connections.

Also, Read: Lennox SL22KLV Heat Pump Error Code 117: Faulty Pressure Switch Detected

Replacing the Faulty Thermistor

When replacing the thermistor, you’ll need to identify the cause of the failure to guarantee you’re addressing the root issue.

You’ll then need to locate the faulty thermistor, which is typically found near the compressor or outdoor coil.

Identifying Failure Causes

If you’re experiencing the Lennox heat pump model error code 120, you’ve likely already consulted the user manual or online resources, which is a great first step.

Now, it’s crucial to identify the underlying causes of this serious error.

Thermistor Failure can occur due to various reasons, leading to a communication failure, which in turn triggers the error code to appear.

• Faulty wiring: Check for any signs of physical damage, corrosion, or wear and tear on the wires connecting the thermistor to the control board.
• Moisture ingress: Verify if there’s any moisture or water damage to the thermistor or its connections.
• Electrical surges: Check if there have been any power surges or electrical storms in your area that could have damaged the thermistor.
• Manufacturing defects: It’s vital that the thermistor was faulty right from the start.

Locating Faulty Thermistor

You’ve identified the underlying causes of the Lennox heat pump model error code 120, and now it’s time to focus on locating the faulty thermistor. To do this, consult the unit’s wiring diagram, which typically identifies the thermistor as a temperature-sensing component connected to the control board. The thermistor is usually located near the outdoor coil or compressor of the heat pump.

Replacing Defective Component

The faulty thermistor is now pinpointed, and it’s time to swap it out with a new one.

You’ve identified the defect, and replacing the component is the next step in the repair process.

• Disconnect power: Verify the heat pump is turned off and unplugged from the power source to prevent electrical shock.
• Access the component: Remove the panel to access the thermistor, taking note of its location and wiring connections.
• Remove the faulty thermistor: Gently pull the thermistor out of its socket, taking care not to damage surrounding components.
• Install the new thermistor: Insert the new thermistor into the socket, guaranteeing secure connections and proper wiring.

Also, Read: Lennox SL22KLV Heat Pump Error Code 116: Indoor Coil Freeze Protection Activated

Igniter Malfunction and Repair

When your Lennox heat pump model encounters error code 120, the igniter failure is the primary culprit, and you’re left wondering what’s causing the malfunction.

This igniter malfunction is often linked to thermistor failure, which affects the heat exchanger’s performance. As a result, the gas valve and blower motor may not function properly, leading to further issues.

To repair the igniter, you’ll need to inspect the wiring, clean or replace the igniter, and guarantee proper voltage supply. If you’re not comfortable with this process, it’s recommended to contact a professional technician to diagnose and fix the problem.

Preventing Future Errors

Regular maintenance can pay off in the long run, saving you from costly repairs and guaranteeing your Lennox heat pump model runs efficiently.

By staying on top of system components, you’ll reduce the likelihood of thermistor failure and error codes.

• Check refrigerant levels: Low pressure can lead to system malfunctions, so guarantee you’re within the recommended range.
• Inspect electrical connections: Loose connections can cause issues, so tighten them regularly.
• Clean air filters: Dirty filters can reduce airflow, leading to increased energy bills and system strain.
• Schedule annual maintenance with a professional HVAC technician: They’ll catch potential issues before they become major problems, saving you time and money.

Also, Read: Lennox SL22KLV Heat Pump Error Code 115: Compressor Overload Protection Activated

Importance of Professional Assistance

You’re wise to recognize that error code 120 on your Lennox heat pump model requires more than just DIY troubleshooting.

This thermistor failure error code signals a complex issue that demands Repair Intercession from a skilled professional.

Don’t risk compromising your heating and cooling system’s integrity by attempting to fix it yourself.

A professional technician will accurately diagnose the root cause of the error, ensuring a precise and efficient repair.

Their expertise will also help prevent future errors, saving you time and money in the long run.

Troubleshooting Other Lennox Error Codes

While seeking professional assistance for error code 120, it’s equally important to understand how to troubleshoot other Lennox error codes.

This knowledge will help you identify and resolve other potential issues with your heat pump.

Some common Lennox error codes and their solutions are:

• Service Alert Code 207: Check communication between the thermostat and furnace.
• Service Alert Code 411: Check outdoor temperature sensor failure.
• Service Alert Code 225: Check the high-pressure switch function in the furnace.
• Service Alert Code 31: Check connections and wiring between the thermostat and furnace.

Also, Read: Lennox SL22KLV Heat Pump Error Code 114: Compressor Motor Fault Detected

Frequently Asked Questions

What Is the Code 120 on a Lennox Thermostat?

You’re dealing with a Code 120 on your Lennox thermostat, which indicates a thermistor malfunction, pointing to a heat pump issue that requires a Lennox diagnostic to identify the faulty sensor reading, likely causing a temperature discrepancy.

How Do I Clear My Lennox Error Code?

You’re drowning in a sea of error codes, but don’t panic! To clear the code, research the error code, utilize thermostat analysis tools, and follow diagnostic procedure guides; if needed, replace the sensor and consult heat pump troubleshooting tutorials for a fix.

What Does Idle Mode Mean on a Lennox Furnace?

When your Lennox furnace is in idle mode, you’ll notice features like reduced furnace idle times, automatic idle mode functions, and adjustable idle mode settings that benefit your system by maintaining efficiency, minimizing wear, and optimizing performance.

How to Reset Lennox Thermostat?

You reset your Lennox thermostat by restarting its heating cycles, clearing system alerts, and recalibrating temperature controls, ensuring thermostat settings are accurate, allowing the sensor to function properly, and resolving any issues.

Conclusion

By now, you’ve pinpointed the issue with your SL22KLV Lennox heat pump: error code 120 means thermistor failure. You’ve diagnosed the ignition system, replaced the faulty thermistor, and addressed any igniter malfunctions. Remember, a well-maintained system prevents future errors.

If you’re unsure, don’t hesitate to seek professional assistance. With this guide, you’ve taken the first step in troubleshooting common Lennox error codes, ensuring your heat pump operates efficiently and effectively.