If your pump won't prime or it only primes halfway up the pump pot, there is an air leak somewhere on the suction side. That just means the pump is able to pull air from somewhere and its competiting with the water thats trying to be pulled. When this happens you'll see bubbles inside the pump lid or coming out of the return jets. There are a couple different places that you can look to fix the leak.
1. Pump Ld: Ensure that the lid is on tight and that the lid o-ring doesn't need to be replaced. If there are crackes in the o-ring it can allow air to be pulled in. Sometimes getting the o-ring wet or adding a little bit of lube helps to get a better seal.
2. The Nose of the Pump: There is a union on the intake of the pump that can sometimes get lose or need to be inspected. High temp unions have o-rings on the inside that might need to be replaced.
3. Glue Joints: PVC glue breaks down over time and as it does there are little holes that will allow air in. While the pump is running take a dab of silicone and go around each one of the glue joints on the suction side. The pump will suck the silicone into any of the holes and hopefully seal up the leak.
4. Valve O-Rings: Depending on what type of valves you have, there are usually o-rings inside of them that can go back or get crimped. We sell kits that include all of those o-rings and can easily be replaced.
5. Bad Line: If you've tried everything and the pump still won't prime, there's a chance that one of the lines has cracked underground. Its very difficult to prime a pump if this happens. Seek professional help if you think this is the case. Usually you can isolate the one bad line and keep that valve closed while still running the pump off the others.