Abstract: A system and method for monitoring and diagnosing anomalies in a diffusion or dry low NOX combustion system of a gas turbine, the method including storing a plurality rule sets specific to a temperature spread of the gas turbine exhaust. The method further including determining an anomaly in the performance of the gas turbine using at least one of a swirl angle of the exhaust flow, a health of a plurality of flame detectors of the gas turbine, and a transfer of the gas turbine from a first mode of operation to a second lower NOX mode of operation, and recommending to an operator of the gas turbine a set of corrective actions to correct the anomaly.