HI, ABOUT 8 MONTHS AGO I FITTED A GROHE CONCEALED CISTERN PUSH FLUSH AS ABOVE. THE FLUSH WORKS BY AIR PRESURE. THE FLUSH HAS STOPPED WORKING. I HAVE CHECKED THE BUTTON AND IT IS STILL PUSHING AIR INTO THE AIR HOSE. I HAVE PUSHED AIR THROUGH THE HOSE MYSELF USING MY MOUTH AND THE FLUSH STILL...