The advice you have gotten will normally fix your issue. However there is one more thing to try. There is a clean out access at the bottom right of your unit. You can access it by removing the front lower panel. At the bottom right, unscrew the rubber seal and look for dirt, hair or any objects. Take your finger, reach in and make the small wheel spin. It should spin freely.
You will need a small bucket or towel to catch about a quart of water that usually comes out. Also, if there is water in the tub, it will also drain out so you might need a regular size bucket.
