If a chime or bell does not sound when you push the button, follow the steps shown on these pages: Check the button first, then the chime, then the transformer.
All these components are easily repaired or replaced. However, if the wiring is damaged inside walls, replacing it can be very difficult.
Power for a doorbell is supplied by a transformer, usually attached to a metal electrical box in some out-of-the-way location such as a basement, crawl space, garage, or inside a cabinet. Work carefully -- other components, such as thermostats, might have similar-looking transformers. Follow the wires to be sure.
Doorbell wires may be color-coded, but there is no predicting what color goes to which button. Often all the wires are the same color.
Because the bell circuit operates on low voltage, you do not need to turn off power while testing the button or chime. However, the transformer is connected to 120 volts. Shut off power before removing or replacing the transformer.
About 2 hours to diagnose and repair most problems, not including time spent buying the new part
Screwdriver, brush, strippers, multitester, vacuum cleaner
Stripping wires, attaching wires to terminals, using multitester
Short length of wire, steel wool or fine sandpaper, perhaps new button, chime, or transformer
If that does not solve the problem, detach the wires from the terminals. Hold each wire by its insulation and touch the bare wires together. If you get a tiny spark and the chime sounds, replace the button. If you get a spark and the chime does not sound, test the chime (Step 4). If there is no spark, check the transformer (Step 5).
If a chime does not sound or has a muffled sound, remove the cover and clean any dust or gunk. Make sure the wires are firmly connected to the terminal screws. If there is corrosion on the connections, detach and clean the wires and terminals with steel wool or fine sandpaper.
Set a multitester to a low AC reading and touch the probes to "front" and "trans" terminals, then to "rear" and "trans." If you get a reading that is close to the chime's voltage rating, power is entering the chime. That indicates the chime mechanism is not functioning and the chime needs replacing.
Before you replace a transformer, make sure power is reaching it. If the transformer is attached to a receptacle box, insert the tester probes into the receptacle slots. If the transformer is attached to a junction box, carefully remove the cover and test the wires. Remember, these are 120-volt wires.
If the transformer doesn't work, buy a new one with the same voltage rating. Shut off power to the circuit. Open the box and disconnect the transformer wires. Remove the nut that clamps the transformer to the box and pull out the transformer. Wire and clamp the new transformer.