Whisperflo is losing prime.

I have a whisperflo 1.5 hp that just recently started losing its prime. I can get it primed with the water hose and letting the air out of filter. Once it is going, it has a good strong suction on both skimmers. The pressure on the filter gets up to 10+ lbs. But after about 2 hours it will lose the prime. When the pump is turned off, sometimes water has blown the skimmer lids off. It has never done this and i noticed it started doing this after I changed the cartridge filters on the ccp 420. I am wondering if anyone has had a similar problem? Now there is lots of air in the tank and I have to continually bleed the filter, but there isn't any bubbles in the pool returns?
I took the new filters back out and put it back together empty and it still has this problem, lots of air in the tank. I had already thrown the old filters away before I noticed the problem.
I understand the problem sounds like a air leak and I have done a lot of trouble shooting, but I keep thinking there is a simple problem with the filter. The filter does not leak. I have replaced the pump lids, lid o-ring, drain seal and lubed them up. The pressure gauge on the filter is only 1 year old. I have tested the pump and suction side area twice with shaving cream. The impeller is free of any debris and again, once it gets going it has a strong flow. There is some bubbles in the pump basket but it has always been like this.
The wier gates are moving freely and I even took them off. The water is a inch or two above the tile. The water level in the skimmer is never low and does not vortex. The skimmer and drain pipes connected to the pump and have a compool automatic valve. The pool drain and spa drain are both hooked up to the same line and the two skimmers are connected to the other suction side line.
There is a 2nd compool automatic valve on the return side.
There is also a heater that is my 2nd suspicion (but it shouldn't be a problem). I am suspicious because the house has a new tenant and I know he has been messing with the heater.
There is also a booster pump with flexible hosing. It had small drip and I replaced the hosing and connectors.

Anyone have any ideas?

Thanks. Matt.
 
Welcome to tfp, cleanandclear :wave:

Air in the system causing a loss of prime should have nothing to do with the filter.

When it is working, is there air in your pump basket, or does air start to show up in the pump basket?
 
If the problem happens only when the pump is running, it has to be on the suction side of the pump but from your first post, you took care of the usual suspects (pump lid, drain plugs, weir door). But did you disassemble the suction side valve and lube/check the o-rings?
 
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