Lennox Furnace Code E240
Warning
Low flame current while the furnace is running. The control can see flame but the signal from the flame sensor is weaker than it should be.
Manual wording: “Low flame current - Run mode. Check micro-amperes of flame sensor using control diagnostics or field-installed mode. Clean or replace sensor.”
Documented for: EL296UHE and SLP98UHV series
Likely causes, most common first
- Flame sensor rod coated with oxide or scale
- Poor unit ground, which lowers measurable flame current
- Weak or lifting burner flame
What you can safely check yourself
- Check and replace the air filter if it is dirty
- Turn the furnace power switch off for 30 seconds and back on once
When to call a technician
The manual's action is to measure flame sensor current in microamps, clean or replace the sensor, and verify neutral to ground voltage. That is a technician job inside the burner compartment.
A Lennox furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- EL296UHE Service Literature (Corp. 1246-L10), Table 4 - Integrated Control Diagnostic Codes (Lennox Industries Inc., EL296UHE series 96% AFUE two-stage upflow/horizontal gas furnace (EL296UH045XE36B, EL296UH070XE36B, EL296UH090XE48C)) · checked 2026-08-25
- SLP98UHV Service Literature (Corp. 1029-L7), Table 14 - LED 7 Segment Status / Error Code and Integrated Control Diagnostic Codes (Lennox Industries Inc., SLP98UHV series variable-capacity communicating gas furnace (66,000-132,000 Btuh)) · checked 2026-08-25