Your well pump gets its marching orders from the switch mounted on the pressure tank. When the switch acts up (and they all do eventually), you’ll see all kinds of strange behavior (pump won’t turn on, turns on erratically or won’t shut off). Replacing the pressure switch is cheap and takes only about an hour.
Diagnose a cranky switch by rapping on it with a screwdriver handle. If the pump runs (you’ll hear it click) or quits, you’ve nailed the problem. But even if it doesn’t respond, it’s still worth replacing the switch. Replace it with a new one (about $24 at rural home centers and amazon.com).
Switches come in three pressure ranges: 20 to 40, 30 to 50 and 40 to 60 psi. Always replace your switch with one of the same rating (usually printed inside the plastic cover of your old switch). Also buy a new pressure gauge (less than $10) and a 1/4-in. x 6-in. galvanized nipple.
Flip the breaker to the pump switch and check it with a voltage sniffer to make sure it’s off. Then disconnect the wiring (Photo 1).
Close the valve from the pressure tank to the house. Then drain the pressure tank. Next, remove the old switch (Photo 2) and gauge (Photo 3).
Wrap the pipe threads with Teflon tape and reassemble. Install the wiring, close the faucet and repower the pump.