My dishwasher is not cleaning my dishes well, leaving food and redisue on same, changed the knob for the dish rince hole, my wahser is only 2 yrs old,

Try a shop vac, it should suck it clean. I would suggest rincing the dishes before putting in the dishwasher but then what would you expect a Dehumidifier guy say!

1 Scrape and rinse dishes before putting them in your appliance. Small food particles, grease, sauces and bones clog up the system, keeping the dishwasher from properly rinsing your dishes. You don't need to prewash the dishes but be sure to rinse off any solids.
2 Use a toothbrush to clean around the dishwasher door.
Clean around the seal and hinges of the dishwasher. This area often is forgotten and holds a good deal of bacteria and food splash. A tooth- or bottlebrush is the best way to get into the crevices.
3 Clean chunks of food out of the screen and drain at the bottom of your dishwasher, recommended The Family Handyman. If the drain is plugged, the dirty water can't be washed away and ends up back on your dishes. Nut, bean and seafood shells, bits of plastic and small dishes can lodge against the drain, keeping it from doing its job.
4 Unclog the holes in the sprayer arms. If the holes are blocked by food or soap, water cannot freely spray inside the dishwasher to thoroughly clean the dishes. Leftover food on the dishes can make the dishwasher smell.
5 Keep space around your dishes. Overloading a dishwasher keeps it from running efficiently, allowing gunk to build up around the drain and the spray arms.
6 Run your dishwasher as hot as possible to break down food and grease. The recommended temperature is 120 F.
7 Run the dishwasher with vinegar added to neutralize odor. Empty the dishwasher, place a dishwasher-safe cup filled with white vinegar on the top rack, and run a cycle at the hottest setting. If you prefer, use unsweetened lemonade powder or baking soda in place of vinegar.

Clean out the holes on the spray arms, or replace the spray arms.

It is almost always because you have blocked the hole where the sprayer goes up through the middle of the dishwasher. If it cannot pop up the dishes will not only not clean, but the food will just deposit onto the dishes especially the upper rack.

The problem is hard water. Go to www.dishwasherfilter.com. They have a new product out that solves this problem once and for all. It filters the water entering your dishwasher and removes the hard minerals that cause these spots. Very affordable and guaranteed to leave your dishes looking amazing every time.

CAN I RESET MY DISHWASHER

Clean the filter screen at the bottom of the washer basin.

I had an old machine with a similiar problem & I found that food had somehow entered into the arm that spins & sprays out water. The food blocked somewhat the holes which of course means less cleaning.

Buy a couple of bottles of dishwasher majic, run those through and make sure you are not using too much soap.