The booster pump for our spa loses prime. Over the past few years, when we used the spa once every couple weeks (sometime longer) it would catch and run fine. If we hadn't used the spa for many weeks, I would have to re-fill the pump basket once and it would run fine. The last few times, I had to refill the pump basket up to 10 times before it would finally catch.
I had a repairman look at it, and wanted a sanity check on his opinions. He didn't think it was an air leak since it still pumps; he thought an air leak would hamper the pumping capability. He believes it is a stuck back flow valve. Also, he thought it was strange that there is a back flow valve on both sides of the pump, since the pump is not that much elevated from the spa. He wants to replace the first back flow valve (it is up to 20 years old) and remove the second.
I want to make sure the solution fits the symptoms. My first thought: the pump requires the back flow valve to retain prime (although our main pump didn't have a valve until last year). In the past the valve would not completely shut off, and the water would slowly drain back into the pool. Now the valve doesn't close at all.