Upon arrival tech was informed upstairs zone seemed to be stuck open cause it was getting air through vents with downstairs calling. Homeowner also stated this happened once before a year ago. Tech turned on both zones and cycled upstairs 6 different times and each time zone damper closed and opened accordingly. Tested both dampers at zone board and opened and closed accordingly. Tech informed homeowner that system was not recreating issue but suspects it to be the damper causing it to stick. Emailed estimate to replace damper motor to homeowner and they plan to wait and see if it happens again. System is back operational at this time.