So......Brand new pool (see spec's in signature).....When first filled with water, and in regular pool circulation mode, (return valve set at 75%pool and 25%spa) I could set the intelliflo to 1500rpm and water would push through both the pool, and the spa. The spa has an overflow that goes down to the pool. All suction is from pool. There is a check valve on the spa return due to it being +24" in elevation.
All of that is completely normal, right?
Then, about 2 months later, I noticed that water was no longer flowing to the spa. I had to boost the RPM to 2100rpm to get water to go to spa again. Filter pressure had not changed at all, but I backwashed anyway just in case, NO CHANGE! I opened the check valve and made sure it moved freely and had no obstructions. Pool builder is stumped.
I can accept that 1500rpm might be a little slow to run the pump, but I can't understand why it has changed?