If your doorbell stops working, you may inadvertently miss deliveries or leave dinner guests standing on the doorstep for a while. All you need to avoid this situation is a simple tool or two. The most common causes of malfunction--loose wiring and worn-out switches--are the easiest to fix, requiring only a screwdriver. Troubleshooting other problems may require an inexpensive multitester.
If you have another doorbell button, test it. If it works, the transformer has power, and its half of the chime is working.
Unscrew the switch from the house and pull it away to tighten any loose wires.
If that fails, bypass the switch by shorting across the terminals with a screwdriver blade or by removing the two wires and touching them together. If the bell rings, replace the switch. If not, twist the two wires together and move on to the next step.
Connect the two wires to the two terminals; push the wires back into the wall and screw on the switch. If new mounting holes are required, start the holes with an awl and drive in the screws.
Locate the transformer, and inspect and tighten low-voltage wire connections to it.
If neither doorbell works, use a multitester set to the 50-volt AC range to test the transformer. Touch the probes to the two terminals. If the reading is within 2 volts of the transformer's rating, troubleshoot the chime. If not, go on to the next step.
Shut off the power to the transformer's circuit at the service panel, and remove the outlet-box cover. To test for power, pull out the black circuit wire and remove the wire nut. Probe the black and grounding wires with a neon tester. Repeat the test for white and grounding wires. Tighten any loose connections.
To replace a faulty transformer, remove the low-voltage wires. When there is more than one wire at a terminal, tape them together for easier rewiring.
Shut off the power to the doorbell circuit at the main service panel. Remove the outlet-box cover and disconnect the wires from the old transformer, then disconnect it from the box or the box's cover.
Attach and wire the replacement. Connect the transformer's green wire to the bare grounded wire and its other two wires to the black and white circuit wires. Attach the outlet-box cover and secure each low-voltage wire or set of wires under a terminal.
Remove the chime cover, which may snap or screw onto the base, and inspect all wiring connections.
If the connections look good, set a multitester to the 50-volt AC range, then touch one probe to the transformer terminal and the other to the nonworking front or rear terminal. If it fails the test, replace the faulty wiring (see "Replace doorbell wiring," below). If the chime has power but neither doorbell works, replace the chime (go on to steps 3 and 4).
To replace a chime, remove its cover. Disconnect and label the wires for easier rewiring. Remove the mounting screws and the old chime.
Thread the wires into the back of the new chime and mount it to the wall with the provided screws and anchors. Attach low-voltage wires to their respective terminals and replace the cover.
Disconnect the faulty wire at both ends and loosen or remove all accessible wire staples.
Twist together one end of the existing wire to an end of the new wiring and tape the splice, using very little tape. Pull the existing wire to draw the new wire through holes, staples and wall or ceiling cavities. Pull it through one section at a time rather than all at once. Staple as needed.
An inexpensive digital autoranging multitester is very easy to use and comes with detailed instructions. If you have trouble fishing new wire through an inaccessible cavity, don't pull too hard or you may damage the wire. Try splicing and taping a new wire to the old one at that point. Hopefully the damaged section is not inside the cavity. Before deciding to replace a chime, depress the plunger to make sure it isn't stuck. If it is, clean it with alcohol and a cotton swab.
All the wiring in a doorbell is low-voltage and safe except the 120-volt connection to the transformer. Multitesters are easy to use, but using them to test 120- volt or 240-volt circuits when you've set them for low voltage is very dangerous. Read instructions and doublecheck settings before you probe.