Probably has crud under the one way valve letting pressure bleed back to the tank, very common. Remove the hose fittings, clean what you can see, clean strainer screen. After reassembly turn on pump and open a faucet on full, let the pump run a couple of minutes, should take care of the problem. If not the valve may be bad and need replaced.
Dave & Myra
One day your life will flash before your eyes,
make sure it's worth watching!