A monitoring system for a heating, ventilation, and air conditioning (HVAC) system of a building includes a monitoring device and a server. The monitoring device is installed at the building. The monitoring device(i) measures an aggregate current supplied to a plurality of components of the HVAC system and (ii) transmits current data based on the measured aggregate current. The server is located remotely from the building. The server receives the transmitted current data and, based on the received current, assesses whether a failure has occurred in a first component of the plurality of components of the HVAC system and assesses whether a failure has occurred in a second component of the plurality of components of the HVAC system.