I've never had trouble with mine. It's only 2-3 inches below the kettle and starts moving wort as soon as I turn it on. I have 1/2 ID on the inlet and it's 2 feet long. No valves either.
It's possible the pump is cavitating (turning wort into steam inside the impeller). A throttle valve on the outlet might help.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk