Lennox Error Code E155 indicates Refrigerant leak detector sensor #2 communication lost. 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
Refrigerant leak detector sensor #2 communication lost
Unknown
Issue with wiring harness connecting sensor #2 to control board
Check wiring harness and connector for sensor #2; check sensor for damage; fault clears when communication is restored (blower may latch for 5 minutes)
Sensor #2 harness and connector, 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: