Wolfgang,

I assume that you have the automatic rinse solenoid valve and also the manual ball valve to rinse the membranes. I am trying to remember but is it possible that the valve might be before the auto rinse valve. If so the auto rinse solenoid may be stuck. If I am correct, possibly bypassing the auto rinse valve will work for you.

Another thing that may help you is if you run the watermaker every 3-4 days, even for 30 minutes, you can skip the rinsing until you get it repaired.

I am sure that there are some great watermaker mechanics in Ft Lauderdale, but I do not know them.