When the toilet is flushed, new water fills toilet to about half way up, how can i fix the problem and make water stay at normal level?

or if you mean the water in the pan itself. its because there is a blockage in the waste pipe or drain

Older style WC's with flush handles and ball floats can be adjusted easily. On the water inlet valve there is an adjustment screw that determines at what point the float arm shuts off the inlet valve. In your case it sounds like you need to screw it out so the arm comes up further giving you a higher water level.

if you mean in the pan look inyour man hole look at vent pipe to see it is not blocked

Hi there,should be a simple job depending on what type of valve is fitted. it should have some means of adjustment.usually some sort of screw. Brian

You will have to adjust the flow value which operates the float.hope this help,s