How do I plumb in a dishwasher?
Cold fill, the isolating valve, the waste connection and the high loop — and the differences from a washing machine that catch people out.
- Difficulty
- intermediate
- Time
- 1 hr 30 min
- Read
- 3 min
- Safety
- caution
Short answer
Almost all modern dishwashers are cold fill only. Fit an appliance isolating valve on the cold supply, connect the inlet hose hand tight — the rubber washer seals it, not force — and take the waste to a spigot or standpipe with a high loop above the machine. Then run an empty cycle and check every joint.
It is a straightforward job with three connections and one common mistake. Almost everything that goes wrong is either an uncut waste spigot or an overtightened inlet hose.
Safety
What you'll need
- An appliance isolating valve on the cold supply
- The inlet and waste hoses supplied with the machine
- A hose clip
- A spirit level and an adjustable spanner
Step by step
- Check whether it is cold fill.Almost every modern dishwasher is cold fill only, and heats its own water. Connecting one to a hot supply can damage it and often voids the warranty. Check the machine's plate or manual.
- Fit an appliance isolating valve.A valve with a threaded outlet for the appliance hose, fitted into the cold supply. Without one, servicing the machine means turning the house water off.
- Connect the inlet hose hand tight.The hose has a rubber washer in its nut and seals against the valve face. Hand tight is correct — a spanner crushes the washer and the joint weeps.
- Check the washer is present.It sits inside the nut and occasionally falls out or gets left in the packaging. A missing washer means an immediate leak.
- Prepare the waste connection.Cut the blanking cap off the trap spigot if you are using one, or hook the hose loosely into a standpipe with an air gap.
- Clip the waste hose.Push it fully onto the spigot and secure with a hose clip. Dishwasher pumps push hard.
- Create the high loop.Route the waste hose up above the machine's tub level and clip it there before it drops to the waste. Without it, the machine siphons and can fill with sink water.
- Check the hose lengths.Do not extend the inlet or waste hose beyond the manufacturer's stated maximum, and do not join hoses with improvised connectors.
- Level the machine.Adjust the feet so it is level in both directions and sits square in the cabinet. A tilted dishwasher drains poorly and its door seal leaks.
- Plug into an existing socket.Not an extension lead, and not a socket behind the machine that cannot be reached. If there is no suitable socket, an electrician needs to fit one.
- Run an empty hot cycle and watch.Run a full programme with nothing in it, and check the inlet connection, the waste connection and under the machine at fill, wash and drain.
Tips
- Hand tight on the inlet hose. It is the single most common cause of a leaking new dishwasher.
- Pull the machine out and check underneath after the first full cycle, not just at the connections.
- Keep the isolating valve reachable. A valve buried behind the machine is no use in a hurry.
Common mistakes
- Connecting a cold-fill dishwasher to the hot supply — The machine's own heating and its programme timings assume cold water. Hot fill can damage components, ruins some wash phases, and typically voids the warranty.
- Tightening the inlet hose with a spanner — The seal is a rubber washer compressed by hand pressure. A spanner crushes it out of shape and cracks the plastic nut, so the joint drips under mains pressure.
If it doesn't work
Leak at the inlet valve
Cause: Missing or overtightened washer — Fix: Isolate, check the washer is present and undamaged, refit hand tight.
Water on the floor on the first cycle
Cause: Uncut trap spigot or unclipped waste hose — Fix: Cut the spigot open and clip the hose properly.
Machine fills with dirty sink water
Cause: No high loop on the waste hose — Fix: Raise and clip the hose above the tub level.
Machine will not drain
Cause: Kinked or over-long waste hose, or a blocked spigot — Fix: Straighten the run, shorten it to the stated maximum, and check the spigot is clear.
Questions people ask
Should a dishwasher be on hot or cold?
Cold, for essentially all modern machines. They heat their own water and their programmes depend on it. Check the machine's manual before assuming otherwise.
Can I plumb a dishwasher into the same waste as the washing machine?
Yes, using a trap with two appliance spigots or a double standpipe. Each hose needs its own high loop and its own hose clip.