In-ground 24000 gallon pool
Spa with spillover
Water level 1 inch low but still plenty for skimmer ports
Pump behavior the same whether pulling from all pool or all spa
I cleaned and re-lubed the O-ring plus cleaned the cover plate and mating surface on pump housing
Unusual in the last week: I rotated (electric servo) the three-way valve right before the pump without first turning off the filter. But, this was pool <--> spa and I don't think it passes through a closed position.
Also unusual, opening the cleaning port valve (right before the three-way) to suction doesn't change the pump prime.
I don't think it's an air leak.
Can it be anything other than a blockage?
Do pumps go bad (not the motor)?
Since pump behavior is the same for each source would the blockage be in the three-way valve?
The three-way is glued in: can it be disassembled in place?
What about swapping the pump with the identical one right next to it that is used for the spa jets?