In general terms, it is easy to check why the toilet will not flush. Usually the most simple explanation is that the handle has become disconnected from the mechanism contained within the cistern or that the diaphragm has become split or broken.
The first is an easy repair. The lid of the cistern only has to be removed and the wire connector placed back in the hole or slot.
The most common form of controlling the water within the cistern is by the use of a ball valve. This allows the water to enter through a pipe, because the large copper or plastic ball on the end of the arm has dropped to the bottom of the empty tank.
As the water rises within the tank, the ball floats upwards and at a predetermined level, the arm operates the shut off valve and the supply stops.
A similar type of valve is the ‘Torbeck valve’, which involves the float travelling up and down a vertical tube, rather than at the end of an arm.
Once the tank is full a siphon, connected to the external handle, allows the water to escape when the handle is depressed. The water is pulled up by a diaphragm within the siphon until it reaches an upper chamber and spills over into the flushing chamber and into the toilet pan.
If the diaphragm is damaged the water will not be lifted into the chamber and the flush will not work until the diaphragm is replaced.