A microwave ablation system includes an antenna assembly configured to deliver microwave energy from a power source to tissue and a coolant source operably coupled to the power source and configured to selectively provide fluid to the antenna assembly via a fluid path. The system also includes a controller operably coupled to the power source and a sensor operably coupled to the fluid path and the controller. The sensor is configured to detect fluid flow through the fluid path and the controller is configured to control the energy source based on the detected fluid flow.