how do you check to see if it still working? mine isn't using much salt any more.

Check to see if there is a salt bridge in the tank. Happened to me once.

Is your water hard? that would be how I would check. You should be able to feel if your water is hard, another test is take unscented medical soap and pit a drop in a vile with water and shake it. lIf you get lots of long lasting bubbles means your water is soft. If the bubbles disappear quickly you have hard water. Thats the same test culligen uses, and they will provide the soap and vile in a test kit.
My water softener also has something on the head unit to show water is flowing. Yours may have the same. Obviously you have water going through but maybe the turbine is not moving to measure the water flow, which results in no regeneration.

thanks!

Never use salt pellets, always crystal salt.