Various implementations include a water heater system. The system includes a variable speed pump. The variable speed pump has having an inlet and an outlet. The system includes a heat exchanger, having an inlet and an outlet. The heat exchanger outlet is fluidically connected to the variable speed pump inlet. The system includes an output temperature sensor disposed downstream of the heat exchanger outlet. The system includes a controller configured to receive a first temperature reading from the output temperature sensor. The controller is configured to control operation of the variable speed pump to adjust an output flow rate in response to the first temperature reading. The controller is further configured to receive a second temperature reading from a recovery temperature sensor on a storage tank. The controller is configured to turn off the variable speed pump upon a determination that the second temperature reading has reached a maximum temperature.