First question I would ask would be:
I would not recommend spending any money on your softener because of the age. However, you might try the following steps to see if you can get it working for free:
First: If the salt has hardened and formed a 'bridge' with a hollow portion at the bottom the softener will not be able to regenerate properly. Salt draws moisture out of the air, so you should not load any softener more than half full of salt. If you suspect a bridge has formed try to break it up with a broomstick, making certain, of course, not to damage the resin tank or the brine tank in the process.
Secondly: Does your unit have instructions for cleaning the venturi on a decal under the salt cover? If the unit never uses any salt your problem may well be a clogged venturi or a bad metering washer, which can fail eventually because of the chemicals in your water. Follow the instructions precisely to disassemble, clean and reassemble the venturi. The water should be off to the house when you attempt this, and several faucets opened to relieve the pressure. Finally slide the bypass to the 'bypass' position so water will not flow down the pipes and out the venturi when you remove the top for servicing. Take note of which side of each part is up, because the parts must be installed with the proper side up to function properly.
Thirdly: Does it have a 'regenerate' button? If it does press and hold the 'regenerate' button until the unit begins a 'Service' cycle. This is an abbreviated cycle to make sure that the valves in the head turn with the motor on top. You should hear the motor and be able to see the gear on the top of the head turning with the top off from both the brine tank and the softener cover. As the motor turns you should hear water alternately filling, and later emptying the brine tank. You should also hear the unit flushing water down the drain during the rinse cycles. If you do not you would probably do well to replace the unit.
Replacing a Kenmore softener with a Kenmore softener should be a relatively easy procedure. I suggest checking the measurement to the center of the bypass (the horizontal part that goes inside the softener head). If a current model is exactly the same height it you can swap the new for the old and keep your old bypass if it is not leaking. Save the new bypass as a spare because all the parts inside may swap for the old if you ever develop a leak.
has manuals and extensive troubleshooting advice with animations. Our Manage My Home website may have the owner's manual as well. You would need to use the full model number of the water softener to access the correct owner's manual. Here is a link for the manual on one model of Kenmore UltraSoft 400 water softener:
If your model matches the one for the above manual (625.388400 or 625.388450), then you can use the information in this manual to help resolve your water softener problem. The owner's manual for your water softener should have extensive diagnostic tests and troubleshooting included in the manual. If you need more help, resubmit your question with additional details including the full model number of your Kenmore water softener.