bryan wrote:
when i flush toilet it continues to flow from the cistern while the cistern
is filling up again. i have replaced old siphon with new one and still the
same problem arises. to stop it i have to lift up ball cock until cistern
is empty and then it is ok. What is wrong?.

Look closely at the flapper valve. Thats where the water exits to the
bowl, it lifted by a chain from the flush lever.

It should fall back into place when the lever is released and water
flow under the valve drops as the cistern empties.

The seat may be dirty, preventing a proper seal, or the chain may be
twisted stopping it from closing properly.

Replacing it isnt a big job and they arent very expensive.