A dishwasher is one of the easier major appliances to install, typically requiring two simple plumbing hookups, a little wiring and two screws for mounting. It's also lightweight enough that most handy folks swap out a unit without a helper. Yet if this is all true, you might be wondering, then why are so many dishwashers installed improperly? We've all seen dishwashers with doors that rub against the cabinets or those that lurch forward when a full rack is pulled out. The answer is a bit of a paradox: Like painting a house, installing a dishwasher is easy enough that a lot of people will try it with little or no prior knowledge or experience, and some of us just have to learn the hard way. Smarter people read articles like this first.
Water Line Warnings
You have to buy your own water supply hose and fittings for a new dishwasher. What you need is a 3/8-inch O.D. braided steel, flexible water hose with female 3/8-inch compression fittings on both ends. Don't buy one with a garden-hose-sized connection on one end, even if the thing is labeled "Dishwasher Hose." You also need a water line angle fitting for the dishwasher end and a two-port shutoff valve for the water supply pipe under the kitchen sink (if it doesn't already have one). Tighten all connections carefully and check thoroughly for leaks before buttoning up the dishwasher and forgetting about it. A small leak under the appliance might go unnoticed for a long time, wreaking havoc on your subfloor and everything below.
Insufficient Door Clearance
With the door closed, a dishwasher should be centered between the flanking cabinets and have an even reveal at the top (assuming the countertop is level). If your door rubs against a cabinet, remove the mounting screws (see discussion below) and tap or pry the dishwasher over for more clearance, then install the screws in new pilot holes. If the door grazes the countertop, remove the kick plate at the bottom front of the dishwasher, and use channel-type pliers to turn the feet—they have threaded posts for adjusting height—to lower and/or level the unit as needed.
Problems with the Mounting Screws
The only thing holding a dishwasher in place are two screws securing little metal tabs (above the door) to the underside of the countertop. The thickened edge of a laminate countertop is 1 ½ inches. Guess what happens if you use 2-inch screws? Same thing goes for solid-surface tops (such as Corian). So, don't use screws that are too long, and be very careful when driving them, just to be safe.
Granite and other stone countertops present a special challenge, since there's no wood substrate to screw into. Whatever you do, don't try to screw into the stone. Remodeler Tim Hewitt said on Hometalk.com, "The use of side brackets is the normal way to secure a dishwasher in place with a granite top." You can anchor the dishwasher to the flanking cabinets, provided the appliance has side-mount tabs (many newer units do). If not, you can glue a wood strip or two small blocks to the underside of the countertop, then screw the top tabs into the wood (not the stone). In any case, talk to your countertop supplier or installer for recommendations.
Faulty Drain Hookup
Ever called a plumber in a panic because your kitchen sink drain was backing up into your dishwasher? If so, you know that this is every bit as gross as it sounds. This can happen if the dishwasher's drain hose isn't connected to an air gap device or, without an air gap, the hose doesn't make a high bend that reaches above the water level in the sink. Another classic mishap is to connect the drain hose to a garbage disposer but forget to remove the plastic knockout plug inside the disposer's nipple, so the drain line is effectively sealed shut. A tap with a screwdriver and hammer removes the knockout; just remember to fish it out of the disposer before running it.