A building controller for controlling one or more building control components in a building, wherein the building controller is configured for bidirectional communication via a communication network between the building controller and the one or more building control components. The building controller can include a housing, a control unit, and a display unit. The control unit can execute an operating system and a building control application program having a control algorithm. The display unit may be configured to display at least one screen that facilitates user monitoring of diagnostic messages of the operating system of the control unit. Alternatively, or in addition, the display unit can be configured to display a screen to facilitate user entry of operating system parameters and/or a screen to facilitate entry of operating system commands for execution on by the control unit.