Pressure drops when turning pump on and off


Well-known member
Jun 4, 2014
Shrewsbury, PA
I'm new to the pool thing. My 16x32' Radiant was just installed 2 weeks ago so there is much for me to learn.

Our first week with the pool, we didn't have electricity to it, so the pump was off. During that time, a large accumulation of dirt settled on the bottom (as the pool is buried on one side - built into a hill - dirt keeps blowing in). When I finally got electricity running, I immediately began vacuuming the pool. My normal start-up pressure reading was 16psi. After vacuuming about 1/5th of the pool, the vacuum would lose suction and I would check the filter and the reading would be about 21-23, so I would backwash. After backwashing, the pressure would drop back to 16, so I figured "Yay! I'm doing it right!"

When I was finally finished vacuuming, the pressure was at 16, and over the course of this week, has slowly climbed to 20. Today I went out and emptied the skimmer basket, and decided I would have a go at emptying the pump basket for the first time. So I turned the pump off, clogged the hole of the skimmer pipe with a rag, but couldn't get the lid off the pump basket because it was on too tight. Anyway, I gave up, unclogged the hole, and turned the pump back on and VIOLA! The pressure dropped back to 16. I figured it must be because I had just turned it back on, and figured it would probably climb back up to 20 after a little time but now, 4 hours later, it is still at 16 and water is coming out of the return with great force.

So my question is... why did doing nothing but turning my pump off for 20 minutes lower my psi back to normal pressure? Just to be clear, I didn't backwash. All I did was turn the pump off and on.

Thanks for any help!