Circuit breakers turn off the flow of electricity to a circuit when an overload or other type of fault occurs. The breaker itself is quite durable and rarely the cause of a tripped circuit. Circuit breakers are heat-sensing switches that use a bimetal strip and a spring to close a circuit, allowing current to flow. Faults in circuits create heat, which causes the strip to bend. This releases a lever that opens the circuit and cuts off the power until you reset it. Begin troubleshooting at the end of the circuit, not at the breaker.
Check for an overloaded circuit. Most household circuits operate at 120 volts and 15 amps, and are capable of safely drawing 1,440 watts of power. If the total wattage on the circuit exceeds this, the breaker will trip. Add the total amount of wattage from appliances and fixtures on the circuit to make sure it does not exceed the circuit's rating. Most appliances have their wattage printed on them. If the circuit is overloaded, move the offending device to a different circuit or confine appliance use to only a few at a time.
Check for short circuits by unplugging the fixtures or appliances individually and checking to see if the breaker stays closed when you reset it. This will identify an appliance that is causing a specific problem.
Examine each power receptacle and light switch on the circuit for loose or worn wires if the appliances check out. Overheated wires in light fixtures are frequent culprits.
Detect faults in power outlets using a neon receptacle analyzer. If there are no shorts in the switches or outlets, the problem is either the breaker or the wiring behind the walls.
Replace the breaker before calling an electrician to check the wires. Kill power to the service panel before pulling the breaker off its bar. Breakers snap onto a hot bus bar, and you can get a nasty shock if the power isn't cut. Disconnect the black wire leading to the old breaker and attach it to the new breaker. Snap the new breaker into place.
Call an electrician if checking for overloads and shorts and replacing the breaker does not solve the problem.