A method for diagnosing an electromagnetic cooking device includes selecting a frequency from a set of frequencies in a bandwidth of radio frequency electromagnetic waves; setting a subset of a set of radio frequency feeds to output a radio frequency signal of the selected frequency; measuring a forward power level for the subset of the set of radio frequency feeds that is outputting the radio frequency signal; measuring a forward and backward power level for the set of radio frequency feeds; and processing the measurements of the forward and backward power levels to determine an operating condition of the electromagnetic cooking device based on the processing of the measurements of the forward and backward power levels.