Lennox Error Code 276

Priority condition: Service Urgent The furnace is not able to calibrate or the high pressure switch opened or failed to close in run mode. The system will go into Watchguard mode. • Measure operating pressure (inches w.c.). • Inspect vent for blockages, and combustion air inducer for correct operation and restriction. • Check for blocked cold end heater box (CEHB), or condensate drain or drain strainers at outlet of CEHB and cracked hoses. • Check for cracked hoses. • Check levelness of unit. NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace Pressure Switch Troubleshooting” for additional information.