Purchased pool and solar heater with home. Solar heater has an older Pentair controller and valve. There is a check valve on the inlet to the solar heater once the diverter valve ports to heater, no other isolation installed. Seems like heater drains when valve ports to pool since water flows into pool and pump shuts off. I'm thinking it must have vacuum valve installed. Is there a need to add manual isolation valves and or manual drains to the system? Weather is Las Vegas wintertime and not frigid Midwest.