Generic Dishwasher

Each brand of dishwasher conducts the task of washing and drying your dishes in a slightly different way but they have more similarities than differences so this section will be written around all brands of under-the-counter dishwashers.

Features and Options

Size

All dishwashers are basically the same size with standardized outer dimensions so that any brand machine will usually fit in your kitchen cabinets. Some brands advertise extra large tanks. The only way to increase the volume of the tank is to make it taller and shrink down the height of the motor and pump under the tank. There are a limited number of ways to cram two racks of dishes into the tank so claims for having a tank with 25% more volume than the other brands may have little value for you.

Stainless Steel Tank

Many years ago KitchenAid introduced the stainless steel tank. This was a significant feature back then because the coatings other than porcelain were pealing off the tanks and they were rusting through - a terminal problem calling for a new dishwasher. Nowadays you can drag your friends and neighbors over to your dishwasher with a stainless steel tank to try to impress them to make yourself feel better for spending $300 to $500 more to get it. My $300 GE Potscrubber has a coated steel tank that looks as good as the day I bought it 10 years ago.

Water Temperature

Washing with hot water is critical for effective and sanitary dishwashing. The dishwashing detergent requires hot water at a minimum of 130 degrees F to remove food and grease from the dishes. Your dishwasher is connected only to the hot water supply but at the start of the fill cycle there can be one or two gallons of cold, and then warm water before the really hot water gets to the dishwasher. The water temperature may be barely over 100 degrees when the water is cut off after a 3 to 4 gallon fill. Running the hot water until it is really hot gives the dishwasher a good start with water close to the operating temperature. Most dishwashers have a heating coil in the bottom of the tank that is submerged in the water during the wash and rinse cycles. The timer energizes the heater coil during the wash cycle to bring the water up to 120 to 140 degrees F. There is a thermostat in series with the heating coil to keep it energized until the water is heated to at least 130 degrees. Many dishwashers allow you to select higher wash and rinse water temperatures to "sanitize" your dishes. The following is a picture of some of the push buttons on a GE dishwasher that allow selection of water temperatures around 155 degrees F. One should not discount the ability of the dishwashing detergent to sterilize germs and bacteria in 130 degree water. Even though you "sanitize" your dishes, can you imagine how many germs and bacteria you deposit back on the dishes when you put them away or back on the table?

Go to the Gaggenhau website to check out some serious water temperature control in a dishwasher. The water is heated external to the tank and when the first wash cycle is finished, heat is removed from the wash water in a heat exchanger and used to heat the incoming rinse water. This machine is perfectly happy with a cold water supply.

Detergent

The detergent is essential for a good dishwashing and can bring the performance of an inexpensive dishwasher up to that of an expensive one. To do this, you must pick a good detergent. My wife uses either Cascade or Electrasol in the powder form. She doesn't like the tablets or gels because sometimes there is a little left in the detergent cup at the end of the drying cycle which indicates that all of the detergent was not used up in the wash cycle and was actually defeating the purpose of the rinse cycle. Good detergents use an array of chemicals and enzymes to clean your dishes whether your water is hard or soft and then rinse away completely with no streaks on the glassware.

Pumps and Motors

Your dishwasher has a pump to push water through the spray arms during the wash cycle and out the drain hose during the drain cycle. The pump is driven by a motor that, in most cases, is connected directly to the pump. The most common configuration is to stack the pump on top of the motor and position this assembly in the center and in the bottom of the tank. The motor turns one way to pump water to the spray arms and the other way for pumping the water out during the drain cycle. The pump had a rubber seal on its perimeter that kept the water where it belonged. This configuration is used by Sears and Whirlpool and works fine until the seal on the shaft between the pump and motor starts to leak. The motor was history when water with corrosive detergent dissolved the motor windings and shorted it out. A typical Whirlpool pump and motor assembly is shown in the illustration to the right:

I decided to switch from a Whirlpool to a GE in my house to get a configuration where a seal leak wouldn't take out the motor. GE mounts the motor out horizontally from the pump which is positioned under the center of the tank. Sure enough, when the pump sprang a leak, the motor was unaffected and purred right along. Replacing the pump and not the motor is not an option so the whole motor and pump assembly had to be replaced anyway. The GE motor turns in one direction so when the dishwasher needs to move from wash to drain, a big solenoid switches a diverter valve that moves the pump's output from the spray bars to the drain hose.

Maytag took a different path in many of their top-of-the-line dishwashers and drove the pump by a large motor via a belt.

Water Filtering

The objective here is to wash food off the dishes and keep from redepositing the food back on the dishes. The basic filter holds food particles until the drain cycle backflushes them out the drain hose to the disposal. Small particles can be held in suspension easier than large particles so some dishwashers offer multiple filters to clean the water before it is recirculated back onto the dishes. Rinsing the food off under the sink faucet and putting them in the dishwasher before the food dries on them will preclude the need for several stages of filtering.

Food Disposal

It's always hard to justify the food disposal feature in a dishwasher. If the food particles stay in big chunks, the filters can easily snag them and hold them for the drain cycle. If a disposal blade is chopping big food particles into fine ones, they will get past the filters and be circulated back on the dishes. Chopping up food particles before they leave the dishwasher during the drain cycle is duplicating the function of the garbage disposal. Again; rinse the big food chunks into the garbage disposal before you put the dishes into the dishwasher and you won't need the disposal function in your dishwasher.

Number of Spray Bars

Multiple spray bars provide streams of water that blast food off the dishes from all directions. A single bar on the bottom throws water up through all the dishes. The water then falls down to the bottom of the tank to be recirculated. A small bar at the very top can spray down on the dishes. A third bar under the upper rack can theoretically hit the dishes with more force than the spray bar at the bottom. Maytag combines multiple spray bars with high water pressure and volume to blast food off the dishes. By now you can see that most of the above options allow the dishwasher to chisel food off that has glued itself to the dishes and dried. These capabilities comes at a high price and can easily drive the cost above $1000.

Noise Abatement

Any dishwasher throwing water around against the tank has the potential for being noisy. The metal tank walls can amplify the sound much like a loudspeaker. A dishwasher without noise suppression can be an unpleasant thing to be around in the kitchen. All manufacturers of upscale dishwashers apply various forms of noise abatement in their machines. Coating the tank exterior, applying insulating blankets to the top and all sides of the tank and installing sound suppression material in the door and behind the access panel all help keep the noise down. A sneaky way to cut noise is to reduce the water pressure and avoid spraying it on the tank walls and the inside of the door. Steps taken to reduce noise have the side benefit of keeping the heat inside the tank and thus allow the dishwasher to heat the water quicker and sustain high water temperatures. I always covered all exterior surfaces of an inexpensive dishwasher tank with blankets of fiberglass insulation encased in plastic film. I also applied the blankets inside the door and glued fiberglass to the inside of the access panels.

Problem Diagnostics

Water Leaks

A water leak is the most common problem in a dishwasher. A small leak can go undetected for weeks depending on the route that the water takes going away from the dishwasher. I lived in a house once where the kitchen floor sloped toward the outside wall. We knew something was wrong when we noticed a swath of dead grass six feet wide leading from the kitchen window to the street. The dishwasher detergent was so corrosive that it was dissolving the kitchen floor in front of the dishwasher. Remove the front access panel to isolate the source of the leak.

Water leaking from the center.
Water leaking from the left side during fill.
Water leaking from the drain hose area during pump out.
Water leaking out the front and under the door.

Doesn't Clean the Dishes Like it Used To

Is your dishwasher not cleaning as well as it used to? This can be caused by a wide range of problems but some of the more likely ones are covered here.

Doesn't Make it Through all the Cycles

Not making it all the way through to the drying cycle is usually an indication that the timer motor has seized. Skipped cycles are also the result of a failed timer. Replacing the timer is required in both cases.

Detergent Doesn't Dispense

Detergent dispensers are usually implemented by providing a spring loaded door over a detergent cup in the dishwasher door. The door is cocked by closing it and thus tensioning a spring. A door trigger is set when the door is fully closed and is tripped by the timer energizing a solenoid. A broken or corroded spring is usually the reason the door won't open. The spring needs to be checked and, if necessary, replaced.