Toilet cistern double flush

[foundry]

Help -
My conventional toilet cistern has now started to do a second flush when the cistern refills without pressing the handle. This has only started to happen recently and no work has taken place since it was new 6 years ago.

Could anyone help me with a possible solution to resolve.

Many Thanks

 

[keego]

Does the cistern overflow to outside or into the pan, if the overflow is into the pan then it sounds like you need to replace the washer in the ball valve.

 

[foundry]

Keego

It does flush inside the pan but when I took the top off the cistern the water supply had shut off tight.

Thanks