Pool pump looses prime only on filter, not on recirc or other settings?

Question

I have a 1 HP pump with a sand filter. I was having trouble with the multiposition valve so I changed it today but this problem was starting before that (though it is worse now). I can run the pump on recirc. and it will run continuously with no problems. If I change to filter, it looses suction within about 5 minutes as if it is not pumping any water through it at all. When I open the purge valve water pressure is minimal when it is running and sucks air in when it looses prime (that part is expected). When running the pressure guage only shows 2-3.

It backwashes and rinses/wastes vigorously without loosing prime, as well.

Any thoughts? I don't see any water leaks. I see only slight bubbles through the return on recirc making me wonder if I've got an air leak but why would it keep running on recirc but not on filter.

Thanks for any help

Answer 1

Hey there! You said you replaced the multi position valve? Was it the whole assembly or just the handle? There are several o rings on the valve, and it sounds as if the o ring has gone out in the filter setting (seeing as this is the most used setting, meaning 10 time the ware on this particular o ring).  If you feel OK with it you can take the valve system off the filter and on the bottom of the valve Assembly there are several screws, open the  valve assembly with it in the filter position and you can see where the water flows through it,  just be careful not to lose anything or forget where it belongs.  there is a o ring for every setting on the valve.  From here you should be able to see how to access the o ring.  Your local pool store or hardware store can sell you another o ring for about 50 cents.  Just be VERY careful when opening the assembly, and take note where everything belongs, cause it need to be put back the same way. If it were me doing it again I would replace as many rings you can. After I replaced mine the following week I had to replace the ring for backwash.  Hope this helps.  You are welcome to email me if you have a problem.

Answer 2

this is just a shot in the dark but mine was doing the same thing and we changed hoses. the ones that were on there was worn out and was collapsing together when we would turn the pump on filter. we got a stronger type hose and replaced them all and works fine now. when you turn it on to filter check and see if your hoses are like smushing together anywhere. good luck to you!

Answer 3

I think your first answerer has a very good suggestion as to what your problem might be.

Other than that, are you sure that the FILTER is O.K.?  It may have come apart in some way that it will accept BACKWASHING FLOW, but not FILTERING FLOW.

Answer 4

Do you backwash on a regular basis? I was asked to look at a friends and found that he didn't backwash regularly. I removed the valve assembly on top and used a broom handle to loosen and stir the sand up. All the sand had settled and most of it had turned hard. I reassembled the valve and went through the backwash and rinse cycle and that seemed to do the trick.  Or, you could always call a pool service company.  Good luck