An energy source of a thermal tissue operating system performs self-tests using simulation heating elements and jaw heating elements in tissue-grasping jaws of a handpiece. Power is supplied to the simulation heating elements and verified, without necessitating connection of a handpiece. Power is also delivered and verified to each of the two jaw heating elements when the handpiece is connected. Voltage and current are measured by peak hold detectors, and the peak hold detectors are tested to verify correct operation. All tests may be combined in a power on self-test (POST).
