hello,i have a pentair 240 ccp filter which fills with air almost immeadiatly when pump is running.no bubbles come out of discharge,no apparent leaks in exposed suction line and return pipes are buried and under a slab.oring on filter appears to be ok.i show little pressure on gauge.flow seems to be strong.i can bleed canister every minute if i want to.should i be concerned?..any other place air could enter?