The most likely thing to go wrong is your check valve but there are other possible issues. If you do the check valve replace it with a brass check valve (I would recomend StraFlow but thats me, they are expensive but very reliable).

Do you have a discharge shut off valve, ball or gate valve? If you do, get the pump running and discharging water. Shut off the valve when your certain you have no more air in the suction line. Turn off the pump and remove your hose bib (assuming you have one) and make sure the water is full to the top. If the water is not 100% to the top fill with a cup of water till it is full. See if the water slowly drops down. If it does check the pump seal, inlet threads and any other possible places where water may drip or seep out. Most likely you wont find any but look very carefully. A handfull of papertowels will help. Also, being on a well, well water will often stain because of minerals in the water. Look for places where the water has leaked in the past.

Second, discharge water into a 5 gallon bucket for 5-10 min when the pump is running and your system is working. Let the water sit for 10+ min and check the bottom of the bucket for sand. There should be none. If one piece of sand sticks in your check valve it will leak slowly over hour or days till the pump loses its prime. This will happen even with new check valves.

If you have found no leaks and no sand (assuming the pump is a self priming pump, irrigation pumps should be) let the pump run and prime itself. This should take between 3-12 min. Running without discharging water for this time frame should not cause any issues. Dont let the pump run more than 16+ min without having its prime. Goulds are very efficent pumps for priming themselves. If the pump has water in it over the impeller it should prime itself in about 8 min on average. (faster on shallow wells) If the pump self primes this quickly and you run the system manually ONLY then I would not worry too much about it and let it be. But, first be sure its your check valve and not sand or a leak.

Good luck,
Tom

thanks Tom but what is a hose bib? The discharge ( output ) is from a standard hose fitting.

A hose bib is what you hook a standard hose to on your house or a pump. The threaded end where the hose goes is universal.

Good luck,
Tom