First, you will get very very little heat out of something that small. Heat gain is a function of the surface area of the collector. Standard panels start around 40 square feet and typically several panels are used at once. That collector is quite small and really won't do much.
There is no one sure to work setting for the diverter valve. If you have a pressure gauge on your filter, adjust the diverter so the pressure goes up 1 psi over it's pressure when none of the water is flowing through the panel. Depending on the size of your pump, you might actually be able to run all of the water through without it going up that much.