IRN R350

Float-controlled valves or equivalent inlet devices should be securely and rigidly attached to the cistern and installed so that the valve closes when the level of the water is not less than 25 mm below the overflowing level of the cistern.  Where the cistern is fitted with an approved alternative to a warning pipe, such as an indicator instrument or visual or audible alarm, the inlet valve is to close when the water level is not less that 50 mm below the overflowing level of the cistern.