i had the same problem.
took it apart, put it back several times, no joy.
what i have found now, a simple cure.
the water will stop if you can get the silver button in the top of the cistern to pop back up. answer.....tap the button with your finger....it comes up. not a lot of pressure needed, about the same as, you would use when typing.
something to keep in my also is, if you have a combi-boiler while water is running elsewhere ie a tap or your toilet, your heating will go off. good luck.