The "NO FLOW" light flashes:

1. When the electrolyzer starts, it is normal for the indicator light to blink, the device needs a few seconds to calibrate. This is quite normal, wait until the calibration is done

2. Variable speed pump, the water flow is too low, it will simply increase the pump speed 

3. The flow sensor or connection plug is broken, you must change the flow sensor   (make a service file)