How to open a toilet cistern — a typical problem for owners of so-called cisterns of the "IDO" system.
If the valve regulation fails on such a cistern, it can easily be opened and adjusted on your own, even though plumbers usually insist at installation that you have purchased a non-disassemblable unit.
How to open the lid
Take a flathead screwdriver or another hard metal object and carefully begin pressing on the chrome plastic ring surrounding the button to rotate it counterclockwise (see photo).
After shifting a few millimeters, the ring will rotate much more easily and can be turned with your fingers.
In practice, what appeared to be a ring recessed into the lid will turn out to be a plastic cylinder.
Unscrew it.
You will then be able to lift the lid. Rotate it 90 degrees sideways and carefully remove the double-ended clip holding the button assembly to the cistern: move one end to the right and the other to the left, rotating the clip around its central axis where the button rod passes through.
How to repair the cistern
The only problem that arises with this type of cistern after 3–5 years of use is that the valve fails to fully shut off the water when the cistern fills.
If you are annoyed by the characteristic trickling sound in the toilet bowl, water condensation on its surface, and the spinning of the water meter impeller, it is time to adjust the valve.
This is extremely simple to do. The issue is typically that the end of the arm locking the valve catches on the very clip that holds the "Do" button actuator in the center of the cistern. Move the arm to the side — away from you (this part rotates) toward the cistern wall, and normal operation will be restored.
Test it by flushing several times, then screw the valve back in place.