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.
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.
What does 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.
Affected Models
- SLP98V
- SLP98
- EL296V
- EL296
- SLP
- SLP
- ELP
- ELP
- NCB
- NPE
- Elite Series
- Elite Series
- Dave Lennox Signature Collection
- Dave Lennox Signature Collection
- ML195
- SLO
- EL296
- SLP98V
- EL296V
- G61
- ELP
- NCB
- NPE
- NPE
- ML195
- ML199
- Elite Series
- Dave Lennox Signature Collection
- Lennox Healthy Climate
- Elite Series
- Elite Series
- Slimline Series
- Slimline Series
- Health Saver Series
- Pace Series
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| High Limit Switch | 34A2011-000 | — |
| Temperature Sensor | — | — |
Related Codes on Same Models
| 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 |