A method and a device for detecting an abnormality of a heat exchanger exchanging heat between a first fluid flow flowing in a conduit and a second fluid flow flowing along a flow path, said conduit and said flow path each having an inlet and an outlet, whereby the method comprises the steps of: establishing at least one parameter representative of the temperature conditions of the heat exchanger, establishing a second fluid inlet temperature, establishing a parameter indicative of expected heat exchange between the heat exchanger and the second fluid, processing the heat exchanger temperature, the second fluid temperature and the parameter indicative of expected heat exchange for establishing an estimated second fluid outlet temperature, employing the estimated second fluid outlet temperature for evaluating the heat exchange between the first and second fluids by comparing the estimated second fluid outlet temperature, or a parameter derived therefrom, with a reference value.