I’m having problems with water in the bottom of my dish washer after the upstairs tub or shower is used. Not all the time, but often enough, we will find about an inch of water. The dishwasher has been in use for several years before this started. The drain hose from the dishwasher runs to my drain under the sink and does have a high loop in it. I do not have a disposal on the sink. I was going to install an air gap but wanted to be sure that was the correct thing to do. Should there be some type of check valve in the dishwasher or drain line to stop water from going back into the dishwasher ?? Thanks for any suggestions !!
Funny thing, I just had a similiar service call yesterday. I found that the discharge hose from the dishwasher to the kitchen drainline had shifted somehow and now was pinched off, leaving some water in the bottom of the dishwasher. Check the discharge hose for any pinching or their could also be a blockage inside the line itself. If you can disconnect the discharge from the plumbing and aim it into a pail. Then run the dishwasher so that it fills and then discharges, you can see by the flow into the pail if there is an obstruction inside the hose itself.. I’ve never heard of installing a checkvalve in a discharge line. The pump itself may be failing, or not working propery as well. Good luck.