Lennox Error Code E164 indicates Low GWP test (test mode activated). 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
Low GWP test (test mode activated)
Unknown
Low GWP test button engaged
Low GWP test mode activates when button is pressed; normal operation resumes and code clears automatically after 1 minute
Control board test circuit
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: