rustyspa

Hi On my 1999 Caldera Utopia model lately when I turn on main jet pumps the circulation pump stop running and makes a humming noise. I turn off the power and open the panel and remove the hose and let some water out and replace it the pump runs again. I done this 2 times now. Any idea what could be the problem? Is there air getting in the system once I start the jets? Is the impleller the problem? thanks