replace syphon?

Graham, if the cistern sits on the loo directly then you will have to take the cistern off the wall to undo the back nut which holds the siphon on to the cistern.
If alternativley it has a pipe which connects the cistern to the pan then you will see Two nuts, one fixes the siphon to the cistern the other connects the pipe to the siphon.
You need to switch off the water and prepare to catch the water once you have slackened off the siphon/cistern nut. You will need a replacement siphon (similar but generally universal) and PTFE tape to make the seals again (wrapping them generously 5-6 times depending.. ) good luck with the silicone it usualy gives after a while...

Pedro
December 2010

You don't need to remove the cistern,you replace the syphon in-situ.

Rich
December 2010