Cooktop appliances are provided. A cooktop appliance can include a gas burner; a manifold having a gas input; a primary line extending between the manifold and the gas burner, wherein the primary line operates as a non-modulated minimum gas flow line when the cooktop appliance is in an automatic mode; a secondary line extending between the manifold and the gas burner, wherein a gas flow rate of the secondary line is controllable by a flow control valve; a primary valve in fluid communication with at least the primary line; and a control system including: a sensor configured to detect a temperature corresponding to the gas burner; and a controller regulating: (i) the flow control valve in response to the detected temperature to achieve a desired temperature, and (ii) the primary valve when the flow control valve is closed and the detected temperature exceeds the desired temperature.