Pump can’t hold prime once deep end/main drain open?


Jul 21, 2019
Hi all! I’m not super pool savvy so I’m bound to get a lot of the terminology wrong, but here goes. We went to open our 28,000 gallon in ground pool a week ago and had a lot of trouble getting it primed. Eventually with a lot of time and effort, we got it to the point that it holds prime with the two skimmer lines open (the two on the right). However, every time we try to go to the next step and open the deep end (The one on the left), we lose prime-the water stops flowing into the pump basket altogether. We got it to the point where we can open the deep end line very slowly, a half inch at a time, and it will hold and keep pumping water out, but eventually at about the 2/3 open point, it will again lose prime completely. Sometimes it will go for 15-20 minutes before this happens.
We had a friend of a friend who’s a pool guy come out and look at it and he said he doesn’t see anything wrong. He took a blower and said he got a ton to blow back out (or something? I wasn’t here) so he doesn’t think there is any kind of leak anywhere. He said to keep opening the deep end a half inch at a time, but we’ve probably spent 6+ hours trying to do that with no real improvement beyond this point.

Any ideas on what could be causing this, or things we can try? I’ve tried to google this but must not be describing it well because my searches come up empty. Thanks in advance!



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

I also think it is a suction side air leak. It could be anywhere, but my first guess would be the "O-Ring" under the pump lid.

I used to have a super pump and since the O-Ring is not round, but more square, I found it was pretty easy for it to leak.

When you lube it up, it gets stretched and then no longer fits.. It also seemed to be that the knobs that hold the lid down had to be tighter than I thought they should..

It is much harder to suck water from the main drain than it is from the skimmers.

Other places I would check would be the union in front of the pump, as well as the weird plug at the top right of your return valves.


Jim R.


TFP Expert
Mar 2, 2011
It might be a leak in the main drain line underground.

Did it work last year?

You're probably going to have to pressure test the line.