Lennox Error Code E204 indicates Gas valve mis‑wired. Start by checking the most common and safe items identified in the troubleshooting section. If the code returns after those checks, professional diagnosis is recommended.
Easy
Gas valve mis‑wired
Unknown
Gas valve wiring incorrect
Check gas‑valve operation and wiring; error clears when repaired
Gas valve
Call an HVAC technician if the error persists after completing the recommended basic troubleshooting steps or if the system repeatedly locks out.
Disconnect power before inspecting the equipment. Never bypass safety devices or operate the system if you suspect unsafe conditions.
Learn more about the furnace components and operating conditions commonly associated with diagnostic error codes: