--- title: "Water Supply and Hot Water Temperature" description: "What the supply line should look like, how to measure the water reaching the machine, and why 120°F is the figure to aim for." url: "https://dishwasherrepair.center/guides/water-supply-and-hot-water-temperature/" date_modified: "2026-09-25" --- Installation and setup # Water Supply and Hot Water Temperature Dishwasher water temperature starts at the water heater: most installation manuals want hot water at about 120°F reaching the machine, and CPSC recommends 120°F at the heater to prevent scalds. The dishwasher heats from there. The supply is a braided line from a shutoff under the sink to an inlet valve behind the kick plate, and it deserves regular inspection. By [DishwasherRepair.center technical team](https://dishwasherrepair.center/authors/technical-team/) Published September 25, 2026 ## At a glance. Most dishwashers in the US are plumbed to the hot line, and what arrives through it shapes how clean the dishes come out. The supply line itself is also one of the likeliest things under the sink to fail. Read the whole guide ### At the tap About 120°F Measured at the kitchen faucet after the water has run hot. ### Heater setting 120°F The setting CPSC recommends to reduce tap-water scald injuries. ### Supply line Braided stainless, 3/8-inch compression From a shutoff on the hot pipe to an elbow on the inlet valve. ### Inspect The line and valve under the sink Look for rust on the fittings, bulges or kinks in the hose, and damp wood. In this guide 1. How water reaches a dishwasher 2. Why the incoming temperature matters 3. Measuring the dishwasher water temperature 4. Temperature and scald safety 5. After plumbing work in the kitchen 6. Questions ## How water reaches a dishwasher The typical American installation takes hot water from the kitchen sink supply. A shutoff valve on the hot pipe in the sink base feeds a flexible line that runs through the cabinet wall and under the tub to the inlet valve at the front of the machine, behind the kick plate. A brass elbow screws into the valve and the line connects to the elbow. The inlet valve is an electrically operated valve that opens when the control calls for water and closes when the fill is done. Everything upstream of it is under house pressure all day, every day, whether the dishwasher is running or not. A few minutes spent under the sink twice a year is the cheapest protection the kitchen has. What to look at: - The braid of the supply line, for rust spots, frayed strands or a bulge - The compression nut at the shutoff, for green or white crust - The valve stem, for a bead of water where the handle enters the body - The cabinet floor under the line, for staining or soft spots - The line where it passes through the cabinet wall, for rubbing against a sharp edge ### What the line is made of Older installs used soft copper tubing, which is durable but kinks easily when the machine is pushed back into place. Most current ones use a braided stainless line with rubber inside, which is easier to route and should be replaced if its braid shows rust or broken strands. ### Water pressure Installation manuals give an acceptable pressure range, commonly from around 20 up to 120 psi. Below the bottom figure the machine may fill slowly enough to show an error; very high house pressure is a job for a pressure-reducing valve at the main, not for the dishwasher. Source: [Whirlpool — Connecting a dishwasher to the water supply](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Installation_Support/Dishwasher_Water_Supply_Connection) — Hot line, shutoff valve, braided or copper line, 3/8-inch compression, 20–120 psi; [GE Appliances — Built-In Dishwasher Installation Instructions](https://products-salsify.geappliances.com/image/upload/s--yxlKQraa--/4e08089748bc59f01329d93f1d3a0456e6018299.pdf) — 3/8-inch copper or braided line at 20 to 120 psi ## Why the incoming temperature matters Detergent enzymes and grease removal both depend on heat, and a machine that starts with lukewarm water spends part of the cycle simply warming it. Many models extend the cycle when the incoming water is cool, which owners notice as a wash that runs far longer than it used to. Some add a heating pause that makes the problem invisible except for the clock. The dishwasher's own heater, or the heater built into its pump, raises the temperature further for the main wash and final rinse. It is designed to top up, not to start from cold. Drawers and compact models are more sensitive to this than full-size machines. Their small tubs hold less water and their heaters are sized to match, so a cool supply takes a larger share of each cycle to correct. - Greasy film left on plastics and pans - Detergent pods that are only partly dissolved - Cycles that run noticeably longer in winter than in summer - Dishes that come out wetter than they did Source: [Whirlpool — How water temperature affects cycle time](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Tips_and_Tricks/How_Water_Temperature_Affects_Cycle_Time) — About 120°F entering; cooler water lengthens the cycle A kitchen thermometer standing in a glass of hot tap water on a stone countertop beside the sink. ## Measuring the dishwasher water temperature A kitchen thermometer and a mug are all it takes. Run the hot tap at the sink until it stops getting warmer, fill the mug and read it after a few seconds. Around 120°F is the target most manuals give; readings in the low 100s mean the water heater, the distance from it, or both, are working against the machine. Take the reading at the time of day the machine usually runs. After evening showers the tank may be partly drawn down, and the dishwasher water temperature at that hour can be several degrees lower than a morning test suggests. ### Kitchens far from the water heater Water left standing in a long pipe cools to room temperature, and the dishwasher's first fill takes exactly that water. Running the sink tap until it is hot, just before pressing start, clears the pipe so the machine gets heated water from the start. ### Tankless water heaters A tankless unit fires only when it senses enough flow. A dishwasher's short, gentle fills sometimes stay under that threshold, so the machine gets cold water from a heater that works perfectly at the shower. Source: [Whirlpool — How water temperature affects cycle time](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Tips_and_Tricks/How_Water_Temperature_Affects_Cycle_Time) — About 120°F entering; cooler water lengthens the cycle ## Temperature and scald safety It is tempting to turn the water heater up to help the dishwasher. CPSC recommends a setting of 120°F to reduce the risk of tap-water scalds, noting that young children and older adults suffer most of those injuries, and hotter water at every faucet is a real hazard in a house with either. The better answer to a lukewarm supply is usually the tap-running habit, a high-temperature or sanitize option on the dishwasher, or a look at the heater's actual output, which drifts as sediment builds up in older tanks. A mixing valve at the heater is another route some households take: the tank runs hotter while the valve blends the outgoing water down to a safe temperature at the taps. That is a plumber's installation, and it changes what the dishwasher receives only if it is set that way. Source: [CPSC — Avoiding Tap Water Scalds](https://www.cpsc.gov/safety-education/safety-guides/kids-and-babies-home/avoiding-tap-water-scalds) — Set heaters to 120°F; young children and older adults suffer most scalds ## After plumbing work in the kitchen A new faucet, a replaced water heater or a repiped kitchen can all change what reaches the dishwasher. Faucet installers sometimes swap a dual-outlet valve for a single one and leave the dishwasher line capped, or connect it to the cold side by mistake. A new water heater often arrives set by the installer rather than at the temperature the old one used. If the dishwasher began washing poorly or running long right after such work, check the mug temperature first, then trace which pipe the dishwasher line actually leaves from. Both take minutes and rule out the plumbing before anything inside the machine is suspected. ## Where to stop Replacing the shutoff valve, reworking the copper to it, or changing the inlet valve under the tub are plumbing and appliance repairs, not adjustments. If the supply line is dripping or its braid is rusted, close the valve and book rather than tightening the fitting harder. Written by [DishwasherRepair.center technical team](https://dishwasherrepair.center/authors/technical-team/). The dishwasher technicians behind the service visits booked here. Each article grows out of problems met in real kitchens and is compared with the maker's manuals and service literature wherever those are published. Sources: [CPSC — Avoiding Tap Water Scalds](https://www.cpsc.gov/safety-education/safety-guides/kids-and-babies-home/avoiding-tap-water-scalds) · [Whirlpool — Connecting a dishwasher to the water supply](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Installation_Support/Dishwasher_Water_Supply_Connection) · [GE Appliances — Built-In Dishwasher Installation Instructions](https://products-salsify.geappliances.com/image/upload/s--yxlKQraa--/4e08089748bc59f01329d93f1d3a0456e6018299.pdf) · [Whirlpool — How water temperature affects cycle time](https://producthelp.whirlpool.com/Dishwashers/Product_Info/Dishwasher_Tips_and_Tricks/How_Water_Temperature_Affects_Cycle_Time) For the heart of your home. ## Questions owners ask. ### Can a dishwasher be connected to the cold line? A few models allow it, and their manuals say so. Most US machines expect hot water, and on cold they run longer and clean less well. ### How often should the supply line be replaced? There is no single interval. Replace it whenever the dishwasher itself is replaced, and any time it shows rust, bulging or stiffness. ### The water at the sink is hot, but the machine says it is not heating. Why? The incoming supply and the machine's own heating are separate. A hot supply with a heating complaint points at the element, the thermistor or the control rather than at the plumbing. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://dishwasherrepair.center/problems/) Problem ### Dishwasher Not Filling With Water 5 causes, cheapest first Problem ### Dishwasher Not Heating Water 5 causes, cheapest first Problem ### Dishwasher Cycle Takes Too Long 5 causes, cheapest first Problem ### Cloudy Glasses and White Residue 6 causes, cheapest first ## When it needs a technician. 68 error codes on this site send owners here first. The repairs on the right are where this guide ends when the checks do not settle it. [ASKO F12](https://dishwasherrepair.center/error-codes/asko-f12/) [ASKO F40](https://dishwasherrepair.center/error-codes/asko-f40/) [ASKO F41](https://dishwasherrepair.center/error-codes/asko-f41/) [ASKO F54](https://dishwasherrepair.center/error-codes/asko-f54/) [Bertazzoni FF](https://dishwasherrepair.center/error-codes/bertazzoni-ff/) [Bertazzoni F3](https://dishwasherrepair.center/error-codes/bertazzoni-f3/) [Bertazzoni F8](https://dishwasherrepair.center/error-codes/bertazzoni-f8/) [Bosch E16](https://dishwasherrepair.center/error-codes/bosch-e16/) [Bosch E18](https://dishwasherrepair.center/error-codes/bosch-e18/) [Bosch E14](https://dishwasherrepair.center/error-codes/bosch-e14/) ### Fill and water valve repair A dishwasher that will not fill, fills too little, or keeps filling, traced through the valve, the float and the supply. ### Heating and drying repair Cold washes, wet dishes and cycles that run for hours, traced to the heater, its sensor or its safety cutout. ### Diagnostic visit The visit that turns a vague complaint about dirty dishes or standing water into one named part and one price. ## More in installation and setup. The drain hose loop, the supply line, leveling, anti-tip brackets and why the disposal connection trips up new installs. [The whole section](https://dishwasherrepair.center/guides/installation-and-setup/) Fitted right the first time ### The Drain Hose High Loop and the Air Gap Why the drain hose has to rise before it falls, how high the loop should be, and when local code calls for an air gap instead. Fitted right the first time ### Leveling a Dishwasher and Its Mounting Brackets How a built-in is fastened under wood and stone counters, why level decides whether the door seals, and how to adjust the feet. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Water Supply and Hot Water Temperature](https://dishwasherrepair.center/guides/water-supply-and-hot-water-temperature/)** **[Book a visit with DishwasherRepair.center](https://dishwasherrepair.center/schedule/)**