Greasy film on glasses, plastic containers that come out wet and cycles that seem to run forever often trace back to the same thing: the water reaching the dishwasher isn't hot enough. Dishwasher makers publish a target for the incoming supply, and it's remarkably consistent from brand to brand. What varies is how close a given house gets to it, and in a long, narrow rowhouse with the water heater in the basement and the kitchen at the back of the first floor, the answer can be "not very."
The target, brand by brand
Whirlpool
Whirlpool's dishwasher temperature page says its machines perform best with incoming hot water of 120°F, and to aim for 120°F at the tap. Whirlpool's dimension guide for the WDT705PAKZ lists the same figure as a supply requirement, 120°F water at the dishwasher, and notes that the model has its own water heating feature but still needs a hot water connection.
GE GLD6500
GE's installation instructions say to adjust the water heater for 120°F to 150°F. Before the first cycle, they have the installer run the sink's hot water and verify the temperature: at least 120°F and no more than 150°F for best wash performance.
Samsung
Samsung's water supply page says your hot water supply should range from 120 to 149°F, and should not exceed 149°F to avoid severe burns. It also notes that inconsistent water temperature can lead to error codes or blinking lights.
Reading them together
The floor is 120°F everywhere. The ceiling sits near 150°F. Whirlpool and GE both frame the check at the tap or at the dishwasher, which matters because water cools on its way through the pipes.
Why temperature matters to a dishwasher
- •Grease and detergent. Fats soften and rinse away far more easily in hot water, and dishwasher detergents are formulated to work in it.
- •Cycle time. Most modern dishwashers have a heater. If the incoming water is cool, the machine spends extra time heating it, which stretches the cycle.
- •Drying. Hotter dishes at the end of the final rinse dry faster, especially plastics, which hold less heat.
- •Steady supply. Samsung's note about error codes is a reminder that the machine expects consistent temperature, not just a minimum.
- •Safety. Water above about 150°F can scald quickly. That's why the ceilings exist.
Why DC homes often fall short
Nothing about the District's water makes it hard to heat. It's the layout of many homes.
- •Long rowhouse runs. In many rowhouses the water heater is in the basement and the kitchen is at the rear of the first floor. The hot line can be long, and it cools between uses. The dishwasher's first fill may be close to room temperature.
- •Basement units and additions. A kitchen in an English basement apartment or a rear addition may be the farthest fixture from the heater.
- •Condo buildings. Some buildings supply hot water from a central plant, others give each unit its own heater in a closet. Either can be set low, and in a building with central hot water the setting isn't yours to change.
Testing it yourself
- Under the sink, confirm the dishwasher's supply tube comes off the hot water valve, not the cold.
- Run the kitchen hot water for 30 to 60 seconds, as Whirlpool suggests, or until it stops getting warmer. Notice how long that takes.
- Fill a cup and measure it with a cooking or candy thermometer.
- If it's under 120°F, check a faucet closer to the water heater. A big difference points to the pipe run. A low reading everywhere points to the heater setting.
- Note the water heater's setting, but on a gas water heater don't change anything except by following its manual.
- Compare with your model: at least 120°F, and no more than 149°F (Samsung) or 150°F (GE).
Simple fixes that help
- •Run the kitchen tap first. Whirlpool recommends running the hot water until it's hot before starting a cycle, so the first fill isn't cold.
- •Use the high-temperature options. On models that offer them, Whirlpool suggests High Temperature or Sani Rinse for heavily soiled loads.
- •Check the water heater setting. Whirlpool says to raise it to 120°F or higher if the tap reading is low, within the safety ceiling above.
When it's ignored
- •Grease film and residue on glasses and containers, even with good detergent.
- •Wetter plastics at the end of the cycle.
- •Longer cycles as the machine heats cold water.
- •Temperature-related codes on some models.
- •On the other side of the range, a burn risk at every hot tap in the house.
Temperature isn't the only supply requirement. Pressure matters too, and appliance water pressure requirements covers how to check it.
Professional work
- •Water heater adjustments. Simple on many electric heaters, but on gas units follow the manual exactly and call a licensed plumber or gas technician if anything is unclear.
- •Mixing valves, recirculation pumps and point-of-use heaters. All are plumbing work, and a point-of-use heater may also need a new circuit from a licensed electrician. DC trade permits listed on the Department of Buildings Instant Permits page are obtained by DC master-licensed professionals.
- •A dishwasher plumbed to the cold line. Moving it to the hot line is a plumber's job.
When the tap reads a solid 120°F and the dishwasher still runs cool, leaves dishes dirty or takes hours to finish, its own heater, thermistor or control is the next suspect. Our dishwasher repair technicians can test each one.
Sources
- •Whirlpool: Dishwasher Water Temperature Troubleshooting (120°F target; tap test; water heater and cycle tips)
- •Whirlpool: WDT705PAKZ dimension guide (120°F water at the dishwasher; hot water connection required)
- •GE: GLD6500 installation instructions (120°F to 150°F)
- •Samsung: Dishwasher water supply requirements (120 to 149°F; burn warning; error codes)