Toilet seemingly impossible to repair... constant water running in to pan

Hi,

Our toilet is running water into the pan constantly. It seemed easy to fix: Remove the 'flush' and replace with a new one... So I bought a new flush ('universal fitting') but can not install it for the life of me. I've had to put the old one back and now it leaks worse!

I can't fit it because the new flush wants to screw on to the pipe that leads from the cistern to the pan, however, as far as I can tell the cistern and pan and pipe connecting them are one unit. I can't find any fastenings to undo. The flush that was installed is fitted such that it's clipped against the cistern which holds it down with a small amount of downwards force.

Other things I've tried:

* Replace the rubber washer/ring on the flush that covers the pipe leading to the pan: I can't find any way of removing this component, the flush seems to be one unit that can't be dismantled.

* Find a replacement of the same flush. There are no distinguishing brand name, part number etc to identify it or the loo by, I searched but can't find something that looks the same.

flush from above, its pneumatic.



cistern



Flush


Underside of cistern, no apparent fixings (polystyrene is the on bottom of the cistern)


where the flush fits, this part again seems un-removable:




Help please.

 

The flush valves are not "universal", you have to find out the manufactures name and buy the exact valve for that concealed cistern.

edit could be here
https://www.toiletspares.co.uk/oli-74-spares.html

 

1. Water can run from the cistern into the WC pan for one (or both) of two reasons:
1a. The inlet valve, which is float operated, is not shutting off the water, which then runs through the internal overflow (normally the centre of the flush valve) into the pan.
1b. The flush valve (this does not apply to the much more satisfactory siphon type) failing to shut completely.
2. The cistern you have is an "Oli".
3. I'd suggest you look up https://www.toiletspares.co.uk/all-spares.html (all OLI spares), try and identify which of the various flush valves your old one was, and buy the specific valve. Thoroughly clean the seating at the base of the cistern into which the valve's sealing washer sits before fitting.
4. If the problem persists, change the inlet valve.