Lennox E240 Error Code: Low flame current in heating mode
Updated October 2026 · Sourced from Lennox documentation
🧭 Check a few things first
A performance warning. The control reports low flame current while heating.
Is it safe to keep running? Check the steps below first. Call a licensed HVAC technician. Flame sensor service is for a professional.
E240 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| E240 Shown as an E code on the 7-segment display of the integrated control | Low flame current in heating mode | Lennox SL280UHVK two-stage variable-speed furnace (integrated control, 7-segment display) |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Turn the furnace power switch or breaker off for 30 seconds, then back on, and see if the code clears.
- Make sure the manual gas valve to the furnace is on (handle in line with the pipe), following the lighting instructions on the furnace label.
🛑 Stop and call a licensed pro if
- Call a licensed HVAC technician. Flame sensor service is for a professional.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Flame rollout, limit or pressure switch codes that come back after one reset.
- Anything involving the control board, gas valve, flame sensor, igniter or venting.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Lennox code
- Count the LED flashes through the blower door window before you switch anything off. Cutting power can clear the code.
- Replace or clean the furnace air filter.
- Check the thermostat: correct mode, set above room temperature, and fresh batteries.
- Make sure the furnace power switch and breaker are on. If the furnace has locked out, turning the power off and back on once restarts it.
- Make sure the gas valve is in the ON position, following the lighting instructions on the furnace label only.
- On high-efficiency furnaces, look at the outside vent and intake pipes for snow, ice, leaves or nests (look only, do not take pipes apart).
Source: Lennox SL280UHVK Installation Instructions 508553-01 (01/2025), Ignition Control Diagnostic Codes (continued), p.37. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Shaun Cain · Certified HVAC & Refrigeration Technician · Ask an HVAC technician
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