Miniature circuit breakers (MCBs) are fitted in newer consumer units in place of fuses. They have the advantage that they can be manually reset without having to replace wire as in the case of the traditional fuse. The MCBs have either a button or lever that can be flicked to reset it.
The MCB tripping is an indication either that the circuit has been overloaded or that a short circuit has occurred somewhere in the system. Before resetting the MCB it is important to identify what has caused it to trip. Switch off all the appliances connected to the circuit to ensure it is not overloading. Now see Identifying a faulty circuit for more details on finding the problem.
First switch off the main switch on the consumer unit, this is very important. Reset the MCB by either pushing the button or by flicking the lever. Finally flick the main switch of the consumer unit back on. If the MCB immediately resets itself once power is restored, then a fault is still occurring, see Identifying a faulty circuit to try to identify the fault.