A system is disclosed for detecting the occurrence and extent of waterlogging in steam heating coils which consists of a series of two or more sensors disposed to measure temperature at strategic locations on the heating coils of a steam heat coil panel, a recording device which logs and stores the temperature measurement data at pre-defined incremental intervals over a significant length of the steam heating cycle, and a method for displaying and interpreting the data to accurately identify the existence and extent of waterlogging within the steam heating system. The temperature sensors preferably are attached to the outside wall of the steam heating coils and transmit data to an electronic recording device. In a preferred embodiment the data is displayed as a series of line graphs which can be analyzed by the use of described techniques to identify the occurrence and location of waterlogging within a steam heating coil.