See the picture...
http://www.partridges.uk.com/catalog/images/CLC_Cistern_Handle.jpg
The handle turns a square shaft - a nylon bar with holes in it fixes to the shaft - a hook passes through one of the holes in the nylon bar. As you turn the handle the hook pulls up on the syphon mechanism.
Use a bucket to flush the toilet until it's fixed.
Go to your local DIY / Hardware store and buy a replacement Flush Handle - The fancy ones like the one in the picture are not very robust and soon break - plain chromium plated ones are much better and cheaper.
It is easy to fit the new handle - honest.
Good luck...
Peccavi
March 2009
howtomendit.com for free repair help, information and advice.
