How to Replace the Compression Fitting on a Dishwasher

A dishwasher compression fitting uses a tightly compressed connection to attach a dishwasher to the water supply. This type of water pipe connection does not require soldering with a torch but relies on pressure to make a water tight seal. Compression fittings should be replaced if they are leaking or if the copper water supply tube of the dishwasher is corroded or kinked. Replacing a leaking compression fitting will prevent expensive to repair water damage and mold growth from occurring in your home. Properly maintaining a dishwasher so that it is in efficient working condition enhances the value of a property.


Turn off the power to the dishwasher at the circuit breaker box. Shut off the water supply at the kitchen water shut-off valve. Place a bucket under the hot water valve that connects the copper supply line of the dishwasher to the hot water pipe under the sink to catch any water trapped in the supply line when you cut it off. Set a pipe cutter onto the copper supply line, as close as possible to the hot water valve. Slowly spin the tubing cutter around the pipe and tighten the knob on the cutter after every rotation to ensure a square even cut.


Remove the screws that attach the dishwasher mounting brackets to the side of the cabinet, the wall or the underside of the counter. Some dishwashers have brackets screwed to the floor. If your dishwasher has floor-mount brackets, remove the screws that attach them to the floor. Gently and carefully pull out the dishwasher from under the cabinet. Remove the sliding racks of the dishwasher, if you can. Have a helper assist you with tilting the dishwasher onto its back so that you can access the compression fitting. The compression fitting is attached to an elbow on the dishwasher's water-supply line.


Cut off the compression fittings from the other end of the copper supply line -- where it attaches to the dishwasher with a 90 degree elbow -- with the pipe cutter. Run the cutter completely around the pipe as before to make an even cut. Twist a deburring tool around the cut ends of the copper water supply tube to remove any burrs.


Inspect the copper water supply line. If it is kinked, corroded or has visible sings of a leak, it will need to be replaced. If it is relatively good condition, it can be reused.


Unscrew the old dishwasher elbow from the water inlet. Remove any Teflon plumber's tape from the threads of the water inlet. Wrap a new piece of Teflon plumber's tape onto the threads. Screw on the new dishwasher brass elbow onto the inlet until it is hand tight and then finish tightening the elbow with a wrench. Push the dishwasher back into place and reinstall the screws of the mounting brackets.


Slide a compression nut and ferrule onto each end of the copper water-supply line. Insert one end of the copper supply line into the dishwasher inlet elbow and the other end into the hot water-supply valve. Push the ferrule of the compression fitting located at each end of the copper supply line over the threaded ends of the hot water-supply valve or the elbow connected to the dishwasher inlet. Move the compression nut over the ferrule so that it sits right up against the threads of the valve or elbow. Screw on the compression nuts until they are hand tight, then use a wrench to turn them a quarter turn.


Turn on the hot water-supply valve and the shutoff valve to the kitchen sink. Watch for leaking connections at the compression fittings. If they leak, turn the compression nut a quarter turn.