Before a dishwasher is fitted, four things need checking: that it physically fits the space, including the height under the worktop; that its hoses will reach the water valve and the waste; that there is a suitable socket nearby that is not hidden behind the machine; and that the new appliance can actually be carried into the kitchen. When a dishwasher installation overruns or has to be rebooked, it is usually because one of those was assumed rather than measured.
This dishwasher installation checklist is written for the stage before anything is connected — ideally before you order the machine, and certainly before the fitter arrives. None of it involves touching pipework or electrics. It is about looking, measuring and photographing, so the person doing the installation knows what they are walking into.
Measure the Opening, Not the Old Machine
It is tempting to measure the dishwasher you already have and buy something the same size. The more reliable approach is to measure the space it sits in and compare it with the installation diagram in the new machine’s manual, which most manufacturers publish online before you buy.
- Width. Full-size dishwashers are normally designed for a 60cm gap and slimline models for 45cm. Measure at the front and at the back — kitchen units are not always perfectly square.
- Height under the worktop. Measure from the finished floor to the underside of the worktop, at the front and the back. Compare it with the minimum and maximum heights the manual gives for the adjustable feet.
- Depth. Measure to the back wall, then look for anything that projects from it: pipes, a boxed-in section, a socket or the back of a sink unit. The hoses need room behind the machine without being crushed.
- Flooring changes. If new tiles, vinyl or laminate have been laid since the old dishwasher went in, the height under the worktop may now be lower than it was. This is one of the most common reasons a new machine will not slide in.
For a built-in model that sits behind a kitchen door panel, the manual will also show the required aperture and how the furniture door is attached. If you have not yet decided between a built-in and a freestanding machine, our guide to integrated vs freestanding appliances explains what each choice commits you to.
Check What the Open Door Will Hit
A dishwasher door drops down to horizontal and sticks out roughly as far as the machine is deep. In most kitchens that is fine, but it is worth opening the old door, or picturing the new one, and checking:
- whether a neighbouring oven handle, drawer handle or corner unit gets in the way;
- whether an island, a radiator or a door on the opposite side of a narrow galley kitchen leaves enough room to pull the racks out fully;
- whether you can stand beside the open door to load it, rather than having to reach over it.
This matters most when a dishwasher is being added to a kitchen for the first time, because nobody has tested that position before.
How Far Is the Space from the Sink?
Dishwashers come with a fill hose and a drain hose of a fixed length, and the manual usually states how far and how high the drain hose can run. The pump can only push waste water so far; a drain hose that is stretched, extended beyond what the manufacturer allows, or run uphill too high is a common cause of a machine that does not empty properly.
That is why dishwashers are normally placed next to, or very close to, the sink. If the space you have in mind is on the far side of the kitchen, assume the job is closer to a first-time installation than a simple swap, because a water supply and waste may need bringing to that spot. Extension hoses should only be used where the manufacturer approves them for that model.
Look Under the Sink (Without Touching Anything)
Empty the cupboard under the sink and have a look with a torch. You are not trying to work on anything — just noting what is already there so it can be photographed and checked:
- A spare appliance valve. These are small valves, often with a coloured lever, on the water pipe. Is there one free, or is the only one already used by a washing machine?
- A spare connection on the sink waste. Some sink traps have a side spigot for an appliance hose. Note whether it is in use, capped off, or missing altogether.
- Room for the hoses. A crowded cupboard with a water softener, filter or waste bin system may leave little space to route a drain hose correctly.
- Signs of an old leak. Swollen chipboard, staining or a musty smell are worth mentioning before the day, because they usually need dealing with before a new appliance goes in.
If the sink already drains slowly, say so. Adding a dishwasher’s waste to a partly blocked trap tends to make the problem worse rather than better.
Find the Socket
A dishwasher plugs into an ordinary socket, but where that socket sits matters. Check whether it is directly behind the space (which means pulling the machine out to switch it off), in a neighbouring cupboard, or controlled by a switch above the worktop. If the old dishwasher is currently running from an extension lead or adaptor, or the socket looks scorched, cracked or loose, mention it — a new appliance should not go onto either. Where there is no suitable socket within reach, one needs to be added first, which is socket and switch work rather than part of the appliance fit.
Plan the Route In and the Old Machine Out
- Check stairs, lifts, tight turns and door widths between the front door and the kitchen, especially in flats and conversions.
- Decide who is removing the old dishwasher and its packaging. If you want the installer to take it away, ask when you book so it can be confirmed.
- If the old machine is still in place, run it empty and let it finish draining the day before, so less water is left in the pump and hoses.
- Clear the floor in front of the space and the cupboard under the sink, so both can be reached straight away.
What to Send Before Booking
Most of the questions an installer would ask can be answered with a few details sent in advance:
- the make and model number of the new dishwasher, or a link to its installation manual;
- a photo of the space with a tape measure showing the width and the height under the worktop;
- a photo of the pipework and waste under the sink;
- a photo of the socket or switch that will power the machine;
- whether this is a replacement or the first dishwasher in that position, and whether it is freestanding, slimline or integrated.
With that information, it is usually clear whether the job is a straight swap or whether a valve, waste connection, socket or change to the units is needed first. Our dishwasher installation page explains how each connection is made, what is checked on the day and what affects the cost. If a washing machine shares the same sink waste, our washing machine installation checklist covers the checks that are different for that appliance.
