A system and method for controlling the operation of a steam condenser in a power plant which includes a steam turbine, the condenser having: a steam flow path including a steam inlet (4) connected to receive turbine exhaust steam from the turbine steam outlet, a condensate outlet (6) and a heat exchange region (2) located between the steam inlet (4) and the condensate outlet (6); a cooling water flow path having an inlet (12) and an outlet (14) and heat exchange elements (16) for conducting cooling water through the heat exchange region (2), and a non-condensible product removal path (26) having an inlet communicating with the heat exchange region (2) and an outlet located outside of the heat exchange region (2). Control is effected by: measuring (30,32) fluid flow at the steam inlet (4), the condensate outlet (6), the cooling water inlet (12) and the cooling water outlet (14); providing a computer model (42) of the condenser in its normal operating condition, supplying the model (42) with representations of the measured flows at the steam inlet (4) and the cooling water outlet (14), and producing, in the model, indications of the flow at the condensate outlet (6) and the cooling water outlet (14) when the condenser is in its normal operating condition; comparing (44) the indications from the producing step with the measured flow at one of the condensate outlet (6) and the cooling water outlet (14) from the measuring step; and effecting (46) a computerized analysis of the result of the comparing step for providing an indication of the probable cause of differences between the compared indications and flows.