A valve assembly for controlling fuel flow to a combustion appliance, the valve assembly comprising: a valve body having an inlet port and an outlet port, with a fluid path extending between the inlet port and the outlet port; a first valve situated in the fluid path between the inlet port and the outlet port; a second valve situated in the fluid path between the inlet port and the outlet port downstream of the first valve, with an intermediate volume between the first valve and the second valve defined by the valve body; a first valve actuator, secured relative to the valve body, for selectively moving the first valve between a closed position, which closes the fluid path between the inlet port and the outlet port, and an open position; a second valve actuator, secured relative to the valve body, for selectively moving the second valve between a closed position, which closes the fluid path between the inlet port and the outlet port, and an open position; an intermediate pressure sensor in fluid communication with the intermediate volume between the first valve and the second valve for sensing a measure that is related to a pressure in the intermediate volume; a controller operatively coupled to the first valve actuator, the second valve actuator and the intermediate pressure sensor, the controller: identifies a predetermined time duration, closes both the first valve via the first valve actuator and the second valve via the second valve actuator, and identifies a measure related to an initial pressure in the intermediate volume of the valve body; identifies a measure that is related to a pressure change rate in the pressure sensed by the intermediate pressure sensor in the intermediate volume during the time duration; identifies a measure, that is related to a leakage rate based at least in part on the measure that is related to the pressure change rate in the intermediate volume and a measure that is related to the volume of the intermediate volume; compares the measure related to the leakage rate to a valve proving system threshold value that is independent of the valve proving system test duration; and outputs an alert signal if the measure related to the leakage rate crosses the valve proving system threshold value. a valve body having an inlet port and an outlet port, with a fluid path extending between the inlet port and the outlet port; a first valve situated in the fluid path between the inlet port and the outlet port; a second valve situated in the fluid path between the inlet port and the outlet port downstream of the first valve, with an intermediate volume between the first valve and the second valve defined by the valve body; a first valve actuator, secured relative to the valve body, for selectively moving the first valve between a closed position, which closes the fluid path between the inlet port and the outlet port, and an open position; a second valve actuator, secured relative to the valve body, for selectively moving the second valve between a closed position, which closes the fluid path between the inlet port and the outlet port, and an open position; an intermediate pressure sensor in fluid communication with the intermediate volume between the first valve and the second valve for sensing a measure that is related to a pressure in the intermediate volume; a controller operatively coupled to the first valve actuator, the second valve actuator and the intermediate pressure sensor, the controller: identifies a predetermined time duration, closes both the first valve via the first valve actuator and the second valve via the second valve actuator, and identifies a measure related to an initial pressure in the intermediate volume of the valve body; identifies a measure that is related to a pressure change rate in the pressure sensed by the intermediate pressure sensor in the intermediate volume during the time duration; identifies a measure, that is related to a leakage rate based at least in part on the measure that is related to the pressure change rate in the intermediate volume and a measure that is related to the volume of the intermediate volume; compares the measure related to the leakage rate to a valve proving system threshold value that is independent of the valve proving system test duration; and outputs an alert signal if the measure related to the leakage rate crosses the valve proving system threshold value. identifies a predetermined time duration, closes both the first valve via the first valve actuator and the second valve via the second valve actuator, and identifies a measure related to an initial pressure in the intermediate volume of the valve body; identifies a measure that is related to a pressure change rate in the pressure sensed by the intermediate pressure sensor in the intermediate volume during the time duration; identifies a measure, that is related to a leakage rate based at least in part on the measure that is related to the pressure change rate in the intermediate volume and a measure that is related to the volume of the intermediate volume; compares the measure related to the leakage rate to a valve proving system threshold value that is independent of the valve proving system test duration; and outputs an alert signal if the measure related to the leakage rate crosses the valve proving system threshold value.