Hoggercap

Hi I recently bought a house with an inground pool and a solar system on the roof. I have a Goldline control panel where I select the temp I desire. The temp sensor sends data to the control panel, which then opens or closes the valve heading up to the roof. With me so far? When the heater is on, everything looks normal - the valve is completely open. But when the heater turns off, the valve rotates well past 90 degrees (110 - 115 degrees) Is this normal? Is the system designed so the valve goes past the OFF position and opens slightly so there is still a small amount of water flowing through the heater? If not, how do I adjust the valve so that ON is on and OFF is completely off?