I can have the pump on high and everything is going good and I got lots of pressure and everything. The water is going up through the 1 1/2 PVC to the second story flat roof and I got warm water returning, but when I switch the pump to low speed nothing changes for about a min or so and then the water stops flowing. I waited for about five min to see what would happen and nothing. Everything is running, but no water is returning back to my pool.

I switch back to high speed and in about 30 seconds the water comes back on. Tried this several times and same effect every time. My only conclusion is that on low speed the pump does not have enough power to push the water up that high and through 10 solar panels. If you got any solutions, I am up for them. When I had the solar panels on the ground just trying them out it worked on low speed and the water seemed to come out hotter.

I keep wrestling in my mind would it be better to have low speed and hotter water but less flow, or high speed with warm water but more flow. On one had I look at this that yeah, the water is hotter at low speed but I am not putting much water in the pool at a time so it is not really doing much. ( Its a big pool, 18' x 40' oval by 54" high) On the other hand I am adding large volumes of water at higher pressure that is putting in a little cooler water but lots of it and shooting it out really far toward the middle. My thinking is that the water turnover rate is going to be greater at high speed and should bring the temperature up quicker at higher volume and pressure than hotter water at low pressure, and low volume. Sort of like which is going to heat you bath tub up quicker if you start with a tub full of cold water, a small trickle of hot water coming in at 100 degrees or a large full blast volume of 90 degree water. The difference between the low speed (when it was working on the ground was 10 to 11 degrees difference) Right now my water at high speed is coming out at around 90-92 degrees from the solar panels.

Pleased advise how the pump should operate fine on low speed going up 2 stories. From what I gather low speed is 1/3 hp and high speed is 1 hp.

Thanks
Aranon