Northstar Ultra holding water...

The house I bought came with a Northstar Ultra water softener. At first there was no water in the salt tank. About 2 months ago, the unit started holding about 2" to 3" inches of water in the salt tank. To my horror!!! This morning I found the salt tank full of water and my utility room flooded with salt water. I've cleaned up the utility room and removed almost all the water from the salt tank, and performed the recommended maint. found under the lid of the unit. I recycled the unit and it seems to operating correctly, but.. I am assuming all is not well. Any suggestions on what the problem might be? I am going to call the home warranty company... but I would like to have a clue about what may be wrong be for their plumber shows up.
Thanks! Bret
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