Lennox EL296UHV Error Code Low Flame Current: Low Flame Current

What Does Code Low Flame Current Mean?

Error code E240 on the Lennox IFC control board means the flame sensor is detecting a flame current that is below the minimum acceptable threshold. The flame sensor is a small metal rod that sits in the burner flame and sends a microamp signal back to the control board to confirm that gas is actually burning. When the sensor gets coated with carbon, oxidation, or other residue over time, it can no longer conduct that signal reliably.

This is one of the most common Lennox furnace error codes and is almost always caused by a dirty flame sensor. The furnace may still run for short periods — the burners will light, but the board will shut them off within a few seconds because the flame signal is too weak to satisfy the safety circuit. You may notice the furnace starting and stopping repeatedly before eventually displaying this code.

If left unaddressed, the weak flame signal will cause the furnace to cycle repeatedly and eventually escalate to a soft lockout (E270). The good news is that this is one of the easiest and cheapest furnace repairs — cleaning the flame sensor takes about 10 minutes and requires no special skills.

How to Fix It: Clean the Flame Sensor

What You'll Need

• Fine emery cloth (220-grit) or Scotch-Brite pad
• 1/4-inch hex head driver or nut driver
• Flashlight
• Clean dry cloth

Steps

1. Turn off power AND shut off gas supply Switch the furnace power off at the disconnect switch near the unit AND at the circuit breaker. Locate the gas shutoff valve on the gas line leading to the furnace and turn it to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave the area immediately and call your gas company from outside.
2. Remove the furnace access panel Remove the lower front access panel of your Lennox furnace to expose the burner assembly. On most Lennox models (SLP98, EL296, etc.), the panel lifts up and pulls out or is held by a couple of screws.
3. Locate the flame sensor The flame sensor is a thin metal rod (usually slightly bent) mounted near the burners, typically on the opposite end from the igniter. It is held in place by a single 1/4-inch hex screw and has one wire connected to it. On Lennox furnaces, it is usually positioned near the right side of the burner assembly.
4. Remove the flame sensor Disconnect the wire from the flame sensor by pulling the connector straight off — do not yank the wire itself. Then remove the single 1/4-inch hex screw holding the sensor bracket in place. Carefully slide the sensor out of the burner assembly.
5. Clean the sensor rod Using fine emery cloth (220-grit) or a Scotch-Brite pad, gently rub the metal rod portion of the flame sensor until it is clean and shiny. Do NOT use steel wool, as it can leave metal fibers that cause electrical issues. Focus on the section of the rod that sits inside the flame. Wipe the rod with a clean dry cloth to remove any dust or residue.
6. Reinstall the flame sensor Slide the flame sensor back into position, secure it with the 1/4-inch hex screw, and reconnect the wire to the sensor terminal. Make sure the connection is snug.
7. Restore power and test Replace the access panel. Turn the gas supply back on (valve handle parallel to the pipe). Restore power at the disconnect switch and breaker. Set your thermostat to call for heat and observe the startup sequence.

When to Call a Professional

Contact a licensed HVAC technician if:

• The flame sensor is clean but the E240 code continues to appear
• The flame sensor rod appears cracked, bent, or physically damaged
• The burner flames appear yellow, orange, or uneven instead of blue
• You notice a gas smell at any point during the process
• The furnace has additional error codes displaying alongside E240