A complete inspection of doorbell wiring is usually impossible, since most of the wire is hidden inside walls. But some wire is visible in every home, and that’s usually the stuff that gets jolted loose or broken. Inspection takes only a minute. You may find a few inches of wire exposed near the transformer or several yards running through an unfinished basement. Doorbell cable consists of three or more thin wires inside a plastic sheath (Photo 1). Look for areas where the sheath is damaged and also for pinched or badly kinked sections. Sometimes the only way to tell for certain whether wires inside the sheath are damaged is to carefully slice open the sheath with a utility knife. If you find broken wire, strip the broken ends and rejoin them with wire connectors. Often there’s not enough slack in the wire to allow for new connections. In that case, add a short section of wire between the broken ends (Photo 1). A spool of 18-gauge wire is available at hardware stores and home centers. The color of the wire doesn’t matter.
If you have doorbell buttons at the front and back of your house and one of them works, you can be sure that the non-working button or the wiring connected to it is bad.
If you don't find a broken wire, remove the doorbell button by unscrewing it or prying it out of its hole with a putty knife. If the bell rings when you bypass the button (Photo 2a), replace the button. Buttons are available at home centers and hardware stores. If the bell doesn't ring, reconnect and reinstall the button.
When a doorbell works properly, small armature rods inside the chime strike metal bars or tubes to create sound. Sometimes the armature sticks or you have a loose wire. To find out, remove the chime cover. Many covers simply lift off. Others are fastened with latches or screws. With the cover off, make sure the wires are firmly connected to the screw terminals.
You’ll need a test light to check the chime itself. Be sure to get a low-voltage tester. Standard voltage testers look just like the one shown here, but they won’t detect low voltage. Touch the common terminal (labeled “com” or “trans”) with one of the tester probes.
With the other probe, touch the front or back door terminal while a helper pushes the button (Photo 3). If the tester lights up, you know the chime is receiving power and there’s something wrong with the chime itself. Sometimes the armatures are too grimy to move. Clean them with rubbing alcohol and move them with your finger. Then try the button again. If the chime still doesn’t ring, replace it. Label the wires as you remove the old chime and connect them identically to the new chime. Chimes start are sold at home centers and hardware stores. If the tester doesn’t light up when your helper pushes the button, the chime isn’t receiving power because of a broken switch, transformer or wiring.
The transformer, which converts standard household voltage to low voltage, is the least likely component to cause doorbell trouble. It can be located anywhere in your home, but you’re most likely to find it on a metal junction box near your heating/ cooling system or mounted on the outside of your main electrical panel. First, make sure the bell wires are securely connected to the transformer terminals. Then test the transformer (Photo 4). If the transformer is mounted on a junction box, you can replace it yourself. Be sure to turn off the power to the circuit at the main panel and then make sure it’s off by using a non-contact voltage detector before disconnecting wires. If the transformer is mounted on the main panel, we recommend that you hire a licensed electrician to open the panel and replace it.
If none these tests exposes the problem, you can bet that a wire is broken somewhere inside a wall. You might be able to locate and repair the break without tearing into walls, but the odds are against you. So the best solution is a wireless system. With a wireless doorbell, the button sends a radio signal that triggers the chime. On the downside, an electronic chime may not create the harmonious ring of metal, and both of its components require new batteries periodically.