Keeping Doorbells Ringing
Doorbells exposed to weather extremes and frequent use may corrode under their decorative covers and eventually stop working. If your doorbell isn't ringing, check your circuit breakers or fuse box first to make sure that the circuit is operating. A transformer steps the electrical current down to a low voltage, so you can usually work safely around the doorbell without having to turn off the current to that circuit (check that this is the case).
Take off the decorative cover, either by removing its visible screws or by prying it off with a flat screwdriver blade (which sometimes reveals screws that must then be removed). You'll be able to see two wires, each leading to a screw terminal. First, try tightening the screw terminals to see if the wires are loose. Test the button's operation.
If it doesn't work, undo the wires, clean off any corrosion with sandpaper, and touch the bare ends together, being careful to hold the insulated part of the wire. If the doorbell sounds, it means there's a problem at the doorbell's button. You need to buy a new button and connect the old wires to the new button's screw terminals; then screw or snap the button housing back on to the door frame, and/or snap the new decorative cover into place.
Tightening the screw terminals can be a quick fix for a doorbell that's not working because its wires have come loose.
If the button doesn't sound when you touch the wires together, the problem is in the transformer or in the wiring between the transformer and the bell, or between the electrical panel and the transformer. Shut off the electrical power to the transformer, snap off its cover, and tighten the screw terminals in case one or more of the wires have worked loose. Turn the power back on, and test the doorbell.
If it still doesn't work, you'll need to have either the transformer replaced or the wiring checked and fixed. In either case, it's a good time to call in an expert to find the problem.