Abstract: A system for monitoring abnormalities in a heat exchanger having heat-exchange tubes for heating feed water with extraction steam, an inlet and an outlet for the feed water, and a drain cooling zone, includes a process input, an apparatus for calculating the differential pressure between the feed water pressures at the inlet and outlet, an apparatus for computing the heat exchanging performance of the heat exchanger, and judgement apparatus for monitoring the differential pressure and the heat exchanging performance, thereby judging the presence or absence of scale accretion within the heat exchanger end, whenever scale accretion is present, judging the specific locations of the scale accretion in the inner and outer surfaces of the heat-exchange tubes, fluid flow distribution passageways and devices other than the heat-exchange tubes.