Lennox Furnace Code E204
Safety fault
Gas valve mis-wired. The control detects that the gas valve is not wired the way it expects.
Manual wording: “Gas valve mis-wired. Check gas valve operation and wiring. Clears when repaired.”
Documented for: EL296UHE and SLP98UHV series
Likely causes, most common first
- Gas valve wiring connected incorrectly, usually after a service call or valve replacement
- Loose or damaged gas valve wiring harness
When to call a technician
Anything involving gas valve wiring is a technician job. Turn the furnace off and have the valve wiring checked and corrected.
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