What should I do if the display is blank?

Check the following in order: (1) Check the circuit breaker to ensure it is not tripped, (2) Check the power switch at the heating and/or cooling system to ensure it is on, (3) Check that the furnace door is closed securely, and (4) If you use batteries, check that fresh AAA alkaline batteries are installed as marked on the battery holder. (Page 20)