The pressure switch on your well is responsible for automatically sensing the need for more water in your pressure tank and supplying power to the pump. It also shuts the pump off after the pressure in your tank has reached the preset limit. When it fails to perform either function correctly, it's time to remove the switch and install a new one. You don't have to call a plumber for this simple operation. If you know how to use an adjustable wrench and a screwdriver, you can do this one yourself.
Turn off electrical power to the well at the service panel.
Open the faucet under the pressure tank. Allow the tank to empty. If the plumbing underneath the tank is not equipped with a drain valve, open the closest faucet.
Unscrew the acorn nut on the top of the pressure switch and remove the cover.
Use a screwdriver to remove the wires from the switch's four terminals. Remove the ends of the wires from the switch.
Place your adjustable wrench on the hex nut on the underside of the pressure switch. Turn the pressure switch counter-clockwise to remove it. Leave the 1/4-inch nipple underneath the switch in place.
Clean the 1/4-inch nipple's threads with a wire brush. Cover the threads with three wraps of plumber's tape.
Thread the new switch onto the nipple. Tighten the switch with an adjustable wrench.
Connect the two wires from the pump to the terminals marked "T1" and "T2". Put the black wire on "T1" and the white wire on "T2."
Connect the two wires from the service panel to the terminals marked "L1" and "L2." Put the black wire on "L1" and the white wire on "L2."
Place the cover on the switch and tighten the acorn nut by hand. Do not use a wrench.
Close the faucet you used to drain the tank.
Turn the power on at the service panel. Check for leaks as the pressure builds in the tank.