I have been trawling the web on this issue with no success. My water softener (Autotrol 255 by the look of it) started to overfill the brine tank after some cold weather last winter. This is being caused by the air check valve (on the 255 valve body, not in the brine tank) being closed all the time. I can do manual regens by removing the float and catching it before any air get sucked in. I know the ball should float after the regen, but since the last step seems to be to flow hard water into the brine tank, how can this be. The ball will only float in soft water.
In that case you aren't getting water back into the brine tank as you should. The cause would be a blocked injector screen or injector or the internal port between the screen and injector. The ball will only float IF there was water going to the brine tank as part of Refill, which happens during the settle rinse.
Overfilling the brine tank means no or incomplete suction (Brine Draw) leaving more water in the salt tank than should be, and incomplete regeneration, and that is caused by a suction air leak during Brining and then Refill putting back the water that was supposed to be sucked out, overfilling the salt tank. Causes are air leaks in the brine line fittings, blocked injector and or screen. Kinked/blocked drain line or low water pressure.
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CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.