Fuelling machines are used to exchange fuels almost everyday in CANDU plants. The ways to monitor and diagnose them have been requested due to its operational importance. In this paper, a new method to diagnose fuelling machine is introduced especially for the bridge assembly. Since the bridge assembly is in the reactor room, no access is allowed while operating. Therefore, diagnostic signals must be obtained remotely. The currents and the voltages of the electric motors were measured and they were further processed to extract the diagnostic signatures. Motor torque was estimated and examined as a diagnostic signature. It provides the information regarding loads on and movements of the bridge assembly which are the two important variables to evaluate the condition. Finally the developed methods are validated through the experiments performed in the laboratory.