Water running into toilet bowl

[QuestionQuigley]

Water is constantly running from my cistern into the toilet bowl. I understand that the first port of call with this problem is often to try replacing the flush seal? I'd like to try that but need pointers on what part(s) to buy and how to do it.

The toilet was installed by a builder about ten years ago, probably bought from Wickes. Here are pics of the inside of the cistern:

Could anyone advise what type of seal I would need for this type of set-up? A link to one I could buy would be most welcome.

Is it a simple job to fit a new seal, bearing in mind my non-existent plumbing skills? Also, do I need to switch off the water supply to the toilet first?

Thanks for any help.

 

[footprints]

They usually just unplug like a bayonet light bulb, IF you can get a replacement unit or seal (I would replace the unit myself) it is a doddle!
BUT the chances of getting the same one as Wickes bought in a job lot from the far East are pretty slim.
Have a look here, I had an obsolete one (18 months old!) and they supplied a direct replacement that fitted the old bottom piece.
If you cannot get a straight swap it can be a swine of a job, cistern off to replace the whole unit because you cannot plug the new one into the old bottom half.

http://www.shop.lunns.net/flush-valves-14-c.asp