Lennox Error Code 4: High Limit Switch Open
Warning: Your Lennox HVAC system has detected a high temperature and has shut down to prevent damage. Call a professional for repair.
LED Blink Pattern
LED blinks 4 times.
How to Fix Lennox Code 4
- Check if your air filter is clean. A clogged filter can restrict airflow and cause the system to overheat.
- Ensure that all vents are open and unobstructed to allow for proper airflow.
- If the issue persists, do not attempt to open the unit or perform any further troubleshooting. Call a professional HVAC technician.
How to Reset Lennox Code 4
- Turn off the furnace power switch, usually located on or near the unit.
- Turn off the circuit breaker for the furnace. Wait 30 seconds.
- Restore power at the breaker and flip the furnace switch back on.
- Set the thermostat to call for heat. If the error code returns after 2-3 ignition attempts, the fault requires repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Lennox Error Code 4 Mean?
The Lennox 4 error, or High Limit Switch Open, indicates that your HVAC system has detected an abnormally high temperature and has shut down to prevent potential damage to the unit. This is a safety feature designed to protect your system and your home. The high limit switch is a safety device that monitors the temperature of the air leaving your furnace or air handler. If the temperature exceeds the set limit, the switch opens and shuts down the system.
Common Causes
- A faulty high limit switch
- A problem with the temperature sensor
- Blocked or restricted airflow over the heat exchanger
- A malfunctioning inducer motor or draft inducer fan
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| The system is not running | Measure the voltage at the high limit switch (terminal H) | 0 volts |
| The system is running | Check the temperature of the air leaving the furnace or air handler | Below 160°F (71°C) |
Applicable Lennox Models
- Lennox Healthy Climate(dual_fuel)
- Dave Lennox Signature Collection(gas)
- EL296(electric)
- EL296V(electric)
- ELP(electric)
- Elite Series(electric)
- G61(gas)
- Health Saver Series(electric)
- ML195(dual_fuel)
- ML199(gas)
- NCB(electric)
- NPE(electric)
- Pace Series(electric)
- SLO(gas)
- SLP(electric)
- SLP98(gas)
- SLP98V(gas)
- Slimline Series(electric)
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| High Limit Switch | 34A2011-000 | — | Find Part |
| Temperature Sensor | — | — | — |
Related Codes on Same Models
Other codes that affect the same Lennox model families as 4.
| Code | Description | Severity |
|---|---|---|
| 1 | Ignition Failure | Warning |
| 2 | Pressure Switch Stuck Closed | Warning |
| 3 | Pressure Switch Stuck Open | Warning |
| 5 | Flame Rollout Switch Open | Warning |
| 6 | Pressure Switch System Lockout | Warning |
| 7 | Ignition Lockout | Warning |
| 8 | Control Board Error | Warning |
| 9 | Line Voltage Polarity Incorrect | Warning |
| E250 | Lennox Code E250 - Indoor Blower Communication Error | Warning |