Hi Mark,

Thanks for your reply. I did have some weirdness with the filter this spring. (Due to bad instructions from the manufactureer a 2-part "floc" product might have reacted inside the filter instead of in the pool.) But..........just today I followed a suggestion and compared backpressure with the filter set on "Filter" and on "Bypass/Recirculate." The difference is only 1 lb., which indicates pretty free flow through the filter.

I do have a bypass on the heater, but we are wimps and use the heater all the time. As noted above, putting the heater on bypass drops the filter backpressure by around 5 lbs. at high speed and 1-2 lbs. at low speed. With the heater on bypass the low speed is able to (barely) operate the water feature and chlorinator.

The check valve is a Jandy.

I've wondered if something "changed" in the heat pump during the (North Carolina) winter or spring startup. In the fall I disconnected all the plumbing to the heater and covered all the open ends with tie-wrapped screen to keep critters out. I did use a garden hose to flush the heater this spring, running the water in both directions.

(We don't close our pool, so the pump was in use - under timer control - all winter.)

My timer only controls the low speed on the pump, so I'm having to run the pump 7x24 at high speed. I'm now using a robotic cleaner, so I am wondering about changing to a 1-speed motor that the timer/controller could control.

Seems like I'm having to reengineer the system while holding the inground piping, filter and heat pump constant. Any and all suggestions would be appreciated.