Permutit unit, with an Autotrol valve. There's a thing called an "air check valve" that stops air being sucked in from the brine tank once all the brine has been used. This has a little rubber ball; once all the brine has been sucked through, and air arrives, it falls to the bottom of its clear chamber and seals the inlet.
Once regeneration has completed the unit squirts fresh water back into the brine tank through the same pipe.
The trouble is (I think) that the ball floats in brine, but not in fresh water, so when fresh is pushed back the ball sinks and the unit thinks it has air. Next cycle more water into the brine tank... eventually it overflows, and I don't get soft water.
So...
- Should the ball float in fresh?
- Where can I get another one?
Andy