If you have the SWG powered independantly of the pump and are using the internal timer of the SWG, it is possible that the SWG is turning on when the pump is not running, which would cause the "water fault". This is a built in safety to prevent the cell from being powered with no water flow.
It is best to use the "external timer" option on the SWG and wire it to the load side of your pump timer, so it will only turn on when the pump is running.
The flow sensor is built into the cell on your model, so no real way to check it that I know of. Your cell is transparent so you should be able to see if water is flowing through the cell.