My heating or cooling system is not responding. What should I check?

First, verify the system mode is set correctly (press Menu, then Mode to set Heat or Cool). For Heat mode, ensure the temperature setpoint is higher than the actual indoor temperature. For Cool mode, ensure the setpoint is lower than the indoor temperature. Also check that the circuit breaker is on, the system power switch is on, the furnace door is closed securely, and allow 5 minutes for the system to respond.