My geberit model number 131.028 dual flush won't shut off with water and leaks into the toilet bowl

It is a problem with the water inlet valve

https://www.plumbersforums.net/threads/how-to-stop-saniflo-toilet-water-running-into-toilet-bowl.106308/

More here.

https://www.google.com/search?q=Saniflow+Sanistar+wall+hung+toilet+won%27t+stop+filling+bowl+with+water


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The flapper at the bottom of the tank is leaking and needs replacement.

By leaking do you mean onto the bathroom floor, or is water escaping out the flush valve (the part that the Hydroright is seated in) into the toilet bowl. If the former 1) check toilet tank mounting bolts/gaskets for deterioration or looseness. These are usually 5/16"x3" brass bolts with rubber, plastic, and metal washers with a nut. They can be seen protruding through bottom of tank. 2) check flush valve and rubber gasket between tank and bowl. The flush valve is the one that the refill tube goes into and the hydroright seats into.
If you are only leaking water into bowl I would suggest the blue dome gasket ( part of Hydroright kit) is not properly seated properly into flushvalve, and you may have to re-install hydroright (the instructions explain how to remove and re-install) . I broke my existing/old flush valve at the base when trying to install my Hydroright so maybe it was fortuitous that it broke and I had to install a new one. Hope this helps.

Take a close look at the Geberit TM seal...mine had air bubbles in it that prevented a flush seal...and heance a slow leak that caused it to fill-up many times a day and night...see my issue here: https://pierrebridge.wixsite.com/fixit.

All toilet bowls have a preset water level determined buy the design of the internal s-trap and can not be change. However if the water level in the tank is not as high as it should be this will affect the water put into the bowel as the bowel in refilled by the flush valve and if it is set to stop before it get filled to the proper setting the bowl water level may be low.
A quick test is to see if the water level in the tank is up to the line in the tank most all toilet tanks have a line either stenciled or marked with a indentation in the porcelain. Another way is to mark the level in the bowel with tape or a marker then pour water slowly into the bowel not fast enough to flush it wait to see if it stays higher then the mark you made or settles back to that level.

Pressure assisted toilets have a stainless steel tank that refills under lid,if your refilling bowl it only needs to fill trap for smell,the pressure assist does the rest,thats part of the water saving of the toilet,you don't have a lot of water in the bowl

The flush valve is leaking. Replace the gasket and your problem will go away.

Sounds like your toilet is not vented properly. Possilbly something caught in the trap is causing it to syphon

You need to replace the tank flapper valve gasket.

Hi
try to increase the amount of water for each flush .