Low system throughput


Apr 19, 2018
Safety Harbor, Florida
I recently did a make-over on my pool system:

1. Installed new DE filter (was filter type before)
2. Installed new New Heater (had none before)
3. Removed one of two pumps and re-plumbed so the pump will pull/feed either the pool or spa, depending on diverter valve settings. There are two diverter values, one on the intake side before the pump, and one on the output side after the filter/heater.

It all works. However, the amount of water that is moved through the system is now much lower than before. It's enough to keep the cleaner moving, but it seems to be at about 60 percent of the pressure that it was before.

What I have tried:

1. Cleaning the DE filter. It is the Hayward pump filter type, so I bumped it 10 times, then flushed it according to the direction. The pressure according to the filter gauge before was 14, the pressure after was 13. After bumping the pressure did not change. I checked the pressure after the cleaning, and before adding new DE, and it still was 13.

The pump is a 3/4 HP 220 volt Hayward. It was in use before, so it makes no sense to me that the pressure would be so reduced.

I did make one mistake when installing the DE filter in that I let it run for a few hours before adding the DE. I did not realize at the time that this was a bad idea.

I don't think the filter is the problem though, as I added that before I replumbed for just one pump. It was running through the new filter before that, and the pressure was just fine. It was only after I replumped it for the one pump.

Is there some way to test and see where the pressure is being lost? I am not sure what else to do.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

Adding a heater in line will increase the overall resistance of the water flowing back to the pool. I suspect that is your main issue.

As an example... People with SWCGs and no heater, can close the flow switch on the SWCG at about 1000 RPM... People with heaters often have to run at 1500 RPM to close the same flow switch.


Jim R.