Jay, I'm assuming this is a shallow well - 1 1/4" pipe pounded 20 or so feet into the ground? When you replaced the check valve, did you use teflon tape (or teflon compound) on ALL the connection threads? You shouldn't have to fill the output line on the pump - but do need to leave the hose bib open until the water flows continuously from the pump. The 8' probably isn't a problem if it simply represents the static ground water level. It's possible you have a cracked pipe or connection underground, though that's the worst case scenario. Once the water is running from the pump are there any air bubbles in the water stream?

The well was put in by the builder as part of the house package. I wasn't here to watch them put it in. I used teflon tape for the threads on the check valve- about four wraps.

The water running from the well has no visible bubles that I can see and don't hear anything that sounds like air at the sprinkler heads other than at start-up. It looks like I wasted my time replacing the check valve and associated piping. After just one overnight, it has to be primed again. There is no heavy equipment traffic in the area of the well. How is it possible the well pipe could be cracked below ground? I hate to think that I have to put in another well. If I do, how far from the existing one should it be?

Somewhere you have an air leak on the intake side of the pump. Every connection on the intake side of the system is a possible source for the air leak, allowing the water to move back into the well and fill the pipe with air.

If you use a pressure tank and the system is kept pressurized when off, you would find these weak connections when the pump turns off because they would then be under pressure instead of suction and water would start leaking. I've had more experience than I want with this and the difficulty of sealing a connection that just doesn't want to seal, and you never realize it is leaking except when under pressure with the pump off--it just isn't a big enough leak to put visible bubbles in the water, but at 40 or 50 psi, it starts dripping.

Check each connection carefully to make sure it is sealed, working back towards the well. If you have any connections where the pipe slides over a fitting and is held in place with a hose clamp, loosen the clamp, warm the plastic pipe with a butane torch until slightly soft, then put the hose clamp back in place and tighten, and make sure you have a 2nd hose clamp on there also. Follow your way back to the well. It sounds like the pipe coming out of the well runs horizontal, but it will be vertical in the well. Check the elbow where this happens and make sure the connections on each side of the elbow are good. Then pull the pipe in the well. It could be damaged or there could be another foot valve at the bottom of the well which isn't seating due to sand/sediment, and if you have been pumping some sand in the water, the pump impellers could have some damage that prevents the pump from self-priming when turned on. A 1 hp pump can move a lot of water, depending on the size of the well casing and replenishment rate of the water, you could be stirring up sand in the well when the pump is running and the sand has accumulated on the foot valve seals enough to prevent them from fully closing.

Finally, if your pump is located above ground level and the system isn't pressurized, you could be having the water leak off on the outlet side of the pump when it is off with air moving back up the lines to the pump and filling it with air. If the rest of the intake was still filled with water, the pump should self-prime, but again if there has been sand going through with the water, the suction could be compromised enough that the pump will just no longer prime itself.