I've now had 2 pool company guys, a plumber, and several friends try to diagnosis and fix my pool flow problem. All of them say "this is really strange" but none of them have fixed the problem. The plumber said he would come back and start taking things apart, but it would be pricey. The pool guys have suggested it could be: bad header in the heater obstructing flow, something stuck in the drain or skimmer lines, or HP too low on the pump. Here's the deal: The pool primes, the pump runs, but the return flow is terrible as is the suction at the skimmer and drain (almost non-existent). BUT, when I turn the first valve after the output (red valve below), water comes gushing out with a lot of power and the pump starts flying and skimmer sucking etc.
I'm wondering if the water flow is indeed being obstructed at the heater OR maybe that check valve in the middle? Should I put in a bypass around the heater and see how things go? Any advice?