Lennox Furnace Code E125
Hard lockout
The control failed its own self-check. This is an internal hardware error on the furnace control board, covering things like flame sense circuit faults and pin shorts. The control restarts if the error clears.
Manual wording: “Control failed self-check, internal error, failed hardware. Will restart if error recovers.”
Documented for: EL296UHE and SLP98UHV series
Likely causes, most common first
- Hardware failure on the integrated furnace control board
- Flame sense circuit fault on the board
- Electrical noise or a power event that corrupted the control
What you can safely check yourself
- Turn the furnace power switch off for 30 seconds and back on once to cycle power on the control
When to call a technician
If the code returns after a single power cycle, the control board is failing and needs to be replaced by a technician.
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