Adding a dishwasher to your kitchen saves time and effort in your daily routine. Luckily, it’s a manageable project for homeowners with basic plumbing skills. In this guide, This Old House plumbing and heating expert Richard Trethewey walks you through the process of installing a new dishwasher.
Preparing for Dishwasher Installation
Before you install your new dishwasher, make sure you have these tools and materials:
- Adjustable wrench
- Dishwasher tailpiece
- Drill/driver
- Drop cloths
- Electrical tape
- Open-ended wrench
- Pliers
- Polarized appliance plug
- Stainless steel braided water supply hose
- Teflon tape
- Three-way shut-off valve
- Twist-on wire connectors
Shutting Off Water and Power
Always take the following safety precautions when working with plumbing and electrical connections in your kichen.
- Locate the main water shut-off valve and turn it off to stop water flow to the kitchen.
- Switch off the power to the kitchen on your home’s electrical panel.
- Verify that both water and electricity are off before moving forward with the installation.
Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, advises caution when turning off the main valve: “Don’t jerk it… if you ever can’t move that thing, you don’t want to force it because there’s nothing between us and the full city water pressure.” You can identify the main shut-off valve because it’s typically right near the water meter, close to the front foundation wall.
Preparing the Space
The space where you’ll install the dishwasher should be clear. Remove any existing cabinetry if necessary and check that the dimensions of the opening match the specifications of your new dishwasher.
Installing Your New Dishwasher
Once your space is ready, follow these steps to install your new dishwasher.
Set Up the Water Supply
Your first several steps will involve setting up the water supply for your dishwasher. You may not need to follow all these steps if you’re replacing an existing dishwasher:
- Use a wrench to remove the existing shut-off valve on the hot water supply line under the sink.
- Install a new three-way shut-off valve onto the existing hot water supply line. Having separate valves for each fixture is helpful if you need to turn off the water to one for maintenance.
- Reconnect the hot water supply line to the new shut-off valve. Trethewey makes a compression connection using a ferrule and a nut.
- Connect a stainless steel braided water supply hose to the shut-off valve.
- Remove the existing tailpiece attached to the sink’s basket strainer and replace it with a dishwasher tailpiece. Tighten the threaded connections with pliers.
Pro Tip: If you don’t already have a dishwasher, the existing hot-water supply line to the kitchen sink probably has a two-way stop valve with a single outlet to the faucet. To add a dishwasher, you’ll need to replace it with a three-way valve, which has two outlets: one for the faucet (the riser) and one for the appliance.
Make the Dishwasher Connections
Next, make the plumbing and electrical connections:
- Tip over the dishwasher and lay it on its back on top of a canvas tarp.
- Wrap Teflon tape around the male threads of a brass adapter elbow.
- Thread the elbow into the water inlet port on the front of the dishwasher. Carefully tighten the elbow with an adjustable wrench.
- Make the electrical connection to the dishwasher with a polarized appliance plug. Secure the wires with twist-on wire connectors.
- Extend the stainless steel braided water supply hose from the sink cabinet out to the dishwasher. Tape the hose down to the floor with electrical tape.
- Carefully slide the dishwasher into place.
- Connect the water supply line to the dishwasher.
Pro Tip: Before sliding the dishwasher into place, locate the two front-to-back clear paths on the underside of the unit—these channels are designed to keep the copper tubing and electrical wiring safely away from the motor. Measure the distance from these paths to the sides of the dishwasher, then transfer those measurements to the floor inside the bay so you know exactly where to position each line.
Secure the Dishwasher
Now you’re ready to secure the dishwasher in place. Here’s how Trethewey does it:
- Use a drill/driver to screw the dishwasher’s mounting tabs to the underside of the countertop.
- Adjust the leveling legs with a wrench until the dishwasher is perfectly level. Replace the dishwasher’s front panel.
- From inside the sink cabinet, connect the discharge hose from the dishwasher to the dishwasher tailpiece. Secure the hose up as high as possible inside the cabinet to prevent contaminated sink water from backing up into your dishwasher.
Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, explains the importance of the high loop: “Any dishwasher manufacturer insists on one thing, a high loop. That means you run your hose to as high as you can get it right underneath your kitchen countertop height. So now two things happen when the pump shuts off, you now have a column of water strong enough to force its weight down and hold that check valve shut.”
Dishwasher: Testing and Finalizing
After installation, test your work and make any necessary adjustments.
Checking for Leaks
First, check for any obvious leaks:
- Turn the water supply back on.
- Carefully inspect all connections.
- If you spot any leaks, tighten the connections or replace faulty parts as needed.
Pro Tip: Richard Trethewey reminds homeowners that there are multiple layers of shut-off protection in your plumbing system. Beyond the main valve inside your home, every plumbing fixture should have a separate service shut-off valve. If your interior valves don’t hold, there’s also a municipal shut-off valve buried outside near the street, below the frost line—look for it in the ground near your front yard, sometimes hidden in the bushes or under landscaping.
Running a Test Cycle
Next, run a test cycle with an empty dishwasher:
- Plug in the dishwasher’s power cord.
- Turn on the dishwasher and run a short cycle.
- Monitor the dishwasher for proper operation and any unusual noises or leaks.
If all runs smoothly, you’re ready to start using your new dishwasher.
