Error code E05 on the Breville BOV800XL toaster oven is a fault code that indicates a problem with the oven's temperature control system. The purpose of this error code is to alert the user that there is a problem with the oven's ability to regulate temperature and maintain safe operating conditions. The specific cause of the E05 error code can vary, as it can be triggered by a variety of different issues, such as a faulty temperature sensor, control board failure, or wiring issues. However, the purpose of the error code remains the same: to notify the user that there is a problem with the oven's temperature control system and that action is required to address the issue.