A broken water well pressure switch should be replaced immediately. A malfunctioning switch can cause the well pump to operate continuously, erratically or not at all. None of these situations is good for the pump or your home's water supply. Fortunately, well pressure switches are not expensive. Most home improvement centers will have them in stock. These are simple to replace with only a few hand tools.
Turn off power to the well. Never attempt any service or repairs on a live circuit.
Remove the pressure switch cover. The cover on most models is attached with a small acorn nut. Use pliers to loosen this nut. Remove the nut and cover. Set them aside.
Use the voltage meter to check the terminal posts for current. The reading for all terminals must be zero. Do not attempt any repair if the reading is anything other than zero. Instead, contact an electrician before proceeding.
Use a screwdriver to loosen and remove the wires from the switch's terminal posts. These will be labeled: T1, T2, L1 and L2. Replacing these wires in the correct position will be made simpler by labeling them individually with a piece of masking tape before removal.
Loosen and remove the locking nut that holds the conduit to the body of the pressure switch. Remove the conduit and wires from the pressure switch.
Remove the pressure switch from the mounting nipple by rotating it counterclockwise. It may be necessary to use a pipe wrench to loosen the switch. If so, attach the wrench to the metal sides of the housing and apply gentle force until it comes free.
Clean the threads on the mounting nipple with a wire brush. Cover the threads with two or three wraps of plumber's tape or pipe compound.
Thread the new pressure switch onto the mounting nipple and hand tighten.
Insert the wiring and conduit through the mounting ring on the new switch. Secure the conduit to the body of the switch with the locking nut.
Replace the wires onto their respective terminals. Secure the wires by tightening the terminal screws.
Replace the pressure switch cover. Restore power to the well and check for leaks.