For a start look at the cistern.Lifting the lid, check out his device.Under the water, on the bottom, is a stub that provides access water at the sink in the toilet.Drain the water and see how this valve.It is possible that a problem in it.
Check whether the valve is closed.If the plug does not fully close the valve, then find out what prevents this.The rod or chain to pull the plug, can be bent, twisted and hooked on to something.Cap itself, which may be formed as a ball may be damaged or destroyed by corrosion.This usually prevents the complete sealing.In this case, the item must be replaced.
It so happens that the valve is fully closed, but the water
still continues to flow.In this case, lower the level of the float.Typically, the float is made of plastic in the form of a closed container.It moves up and down together with the water level in the reservoir.Find your float.The fact that the lower the level of the float, you lower the water level in the tank and it will not rise above a safety mechanism.Note that if the water level in the tube is too high, then the water is poured through the pipe into the toilet.
How to reduce the level of the float?If the float is designed as a container, then squeeze the metal rod (it is attached thereto), lowering it down so that it is below the water level.If the float is designed as a ball, then tighten the screw located at the end of the bar or rod bend down.
Make the drainage test, try out the new water level.If he still rises above the overflow pipe, reduce it a little bit, but if falls too low, raise the float as long as the level is not optimal.Note that the optimal level of water in the cistern should be 2-3 cm below the overflow edge.