If vinegar no longer works, lemon juice won't either. They are about the same acidity. Baking soda is not going to get rid of the shale buildup. Wrong chemical reaction for that. I would suggest that you try full strength vinegar in the coffee pot. If the thing isn't working, this isn't going to make it any worse. You may just have a particularly heavy build up of lime. I am assuming that you use about a 1/3 vinegar, 2/3 water mix to clean, as that is what I am supposed to use in my machine. If full strength vinegar doesn't work, and try it a couple of times through, try CLR. That is an even stronger acid.
I found this site that has many home-made remedies for cleaning.
Baking soda is another natural, non-toxic cleaning ingredient that does wonders for cleaning a coffeepot among other things. Baking soda is a natural abrasive so it can be used to scrub off stubborn stains and residue similar to the way you'd use Comet or Ajax scrubbing powder.
Sprinkle a bit of baking soda on and around the inside of your coffeepot, then moisten it with water and scrub lightly with a clean moist cloth. Add more baking soda and water as needed until the stains are gone, then rinse thoroughly with clear water.
Lemon juice is a natural source of citric acid, and that is also a non-toxic cleaning and disinfecting substance that's easy to use for cleaning a coffeepot. Add a few tablespoons of pure lemon juice to a coffeepot filled with water, then pour that into the coffeemaker reservoir and run the brewing cycle without any coffee grounds in the basket. Run a second brew cycle with plain water to rinse the system fully before using it to make coffee again.
It may just be time for a new one. Most of the outlet stores have decent prices and I've even seen them on sale at some drugstores (CVS and Walgreens).
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