Lennox EL296UHV Error Code E 240: Low Flame Current

What Does Code E 240 Mean?

Error code E240 on the Lennox EL296UHV indicates low flame current during run mode. The flame sensor is a metal rod positioned in the burner flame that generates a tiny electrical current (measured in microamps) to confirm the burners are lit. When this current drops below the expected threshold during heating, the control logs this alert.

The furnace may continue to operate with this code, but the flame signal is marginal. If the flame current drops further, the furnace will lose flame detection entirely, causing it to shut down during operation and eventually lock out (E273). This code serves as an early warning that maintenance is needed.

The most common cause is a buildup of oxidation, carbon, or silica residue on the flame sensor rod. Over time, this insulating layer reduces the sensor's ability to conduct the small current needed for flame detection. A secondary cause is poor unit grounding — the flame sensing circuit requires a clean electrical ground path to function properly.

Common Causes

How to Fix It: Clean the Flame Sensor Rod

What You'll Need

• Scotch-Brite pad Find on Amazon
• 1/4-inch nut driver or hex-head screwdriver Find on Amazon
• Clean dry cloth Find on Amazon
• Flashlight

Steps

1. Turn off electrical power and gas supply Turn off the furnace at the circuit breaker. Turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). Allow the furnace to cool if it was recently running.
2. Locate the flame sensor Remove the furnace access panel. The flame sensor on the EL296UHV is a thin metal rod mounted near the burner assembly. It has a single wire connected to it and is held in place by one mounting screw.
3. Remove the flame sensor Disconnect the wire from the flame sensor. Remove the single mounting screw holding the sensor bracket in place. Carefully pull the sensor out of the burner area.
4. Clean the sensor rod Gently rub the metal rod with a Scotch-Brite pad until the surface is clean and shiny. Rotate the rod while sanding to clean the entire surface. Wipe with a clean dry cloth to remove any dust or debris. Do not use steel wool, as it can leave metal fibers that cause problems.
5. Reinstall the flame sensor Slide the sensor back into its mounting position and secure with the mounting screw. Reconnect the wire. Ensure the rod extends into the burner flame path and the wire connection is firm.
6. Restore power and gas, then test Turn the gas supply valve to ON (handle parallel to the pipe) and flip the circuit breaker to ON. Set your thermostat to call for heat and let the furnace run through a complete heating cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• E240 returns after cleaning the flame sensor
• The flame sensor rod is cracked or physically damaged
• You also see E273 (soft lockout from flame failures)
• The furnace shuts down intermittently during heating cycles
• You suspect a grounding issue (other electrical anomalies in the home)

✓ Verified against manufacturer service manual — March 2026