LLigetfa
DIYer, not in the trades
Remove the checkvalve at the house and put a reducer and Tee on the end of the pipe. Screw an air valve in one side and a pressure gauge on the other side. Pressurize it with air and see if it holds. If it doesn't, then you have to lift the pump and repeat at the wellhead.Is there a way to test the well pipe for a leak?
What about the bladder tank is there anyway to test it?
Have you confirmed that your air gauge is working right? Try letting some air out so that water can get in. If water still cannot enter the tank, then it is plugged as @craigpump suggested.