no flush woring ?

So what type: High level low level close coupled.
It sound like the diaphram membrane has split.
High and low levels are quite easy to work on.
Don't bother with new diaphram either way you have to take it out if it is not replaceable in situ.
Turn off the water feed to the cistern. Bail out the water. Undo the nut holding the flush tube to base of cistern, remove pipe. Release the diaphram pull rod/wire off the flush handle, undo the syphon nut and remove the syphon replace with new syphon.

Close coupled cistern will have to be removed fom the toilet pan. Again turn off the water bail out the cistern and release the water feed pipe off the cistern,
undo wall securing screws, Undo the bolts holding the cistern to the toilet pan. Undo the syphon nut remove the syphon. Renew syphon. Note the doughnut shaped coupling washer replace that also. reassmble.
If you have no stopvalve in the toilet feed now's the time to add one.

Nobby
February 2009