A method and apparatus for operating a microwave heating apparatus includes a microwave source adapted to feed microwaves to a cavity via a transmission line, including measuring a power of microwaves transmitted from the microwave source to the cavity, receiving operational data indicative of the power supplied to the microwave source, and adjusting at least one of an impedance of the transmission line or the impedance matching between the microwave source and the transmission line based on the measured power of the transmitted microwaves and the received operational data.