This is a new American Standard Cadet 3 toilet. The water runs over the overflow pipe constantly even when set at the lowest water level.

Water in my new American Standard Cadet 3 toilet runs constantly into the overflow pipe even with the water level at its lowest setting.

I'm guessing your float is submerged at this point? And this is a brand new unit.

You probibly had debris migrate to the valve which is blocking it from shutting off completely. Assuming pushing the float to its lowest point doesn't allow it to open enough to pass, you may have to turn water off at the wall shutoff and disassemble the valve inside to check for and remove any debris.

Manually pulling your float device up should shut off the water flow. Does it?

Get a snack and review these videos.

https://www.youtube.com/watch?v=ydXW7D53suw

Pull up the float manually ( with your hand ). See if water stops. If it doesn't stop than there is a debris inside the valve closing mechanism. Close water to the toilet, take fill valve apart, clean rubber gasket, put back together and turn water back ON. See if it closes now

Another thing is that you may have the height of the Fill Valve set too high in relation to the overflow tube. If that's the case, lower the fill valve height to the desired height

..... and just in case: Make sure you are adjusting the lowest / highest float position in relation to the height of water level correctly. Sometimes people confuse those two

Hope that helps

Milo

If all else fails you can replace the whole fill valve with a Fluidmaster 400A for about $10, that should cure the issue.