Fault detection for appliances based on energy consumption data

A fault in a device such as a HVAC (heating, ventilation and air conditioning) unit is detected by 700 receiving an energy consumption signal for the device and 702 calculating the correlation between this and one or more basis functions indicative of a fault. Parameters such as the width W or shape ϴ of the basis function may be varied and correlation intensity computed 704. A correlation intensity above a threshold indicates the presence of the fault characterised by that basis function. The energy consumption may be measured at different times and the basis function may be time windowed. An alert may be generated based on the fault or the appliance may be deactivated or changed to a different operating state. The computation may be performed remotely from the appliance, with consumption data provided by e.g. a current clamp.