Fluid flow systems can include one or more resistance temperature detectors (RTDs) in contact with the fluid flowing through the system. One or more RTDs can be operated in a heating mode and a measurement mode. Thermal behavior of the one or more RTDs can be analyzed to characterize a level of deposit formed on the RTD(s) from the fluid flowing through the system. Characterizations of deposition on RTDs operated at different temperatures can be used to establish a temperature-dependent deposition profile. The deposition profile can be used to determine if depositions are likely to form at certain locations in the fluid flow system, such as at a use device. Detected deposit conditions can initiate one or more corrective actions that can be taken to prevent or minimize deposit formation before deposits negatively impact operation of the fluid flow system.