Lennox Error Code E125 indicates Control failed self‑check / internal error / failed hardware. 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.
Professional Required
Control failed self‑check / internal error / failed hardware
Unknown
Hardware problem on integrated control board
Cycle power on control; replace control if error prevents service and is persistent; cleared 300 seconds after fault recovered
Integrated control board
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: