Washing Machines & Dishwashers

Washing machines and dishwashers are plumbed in the same way. The only difference is that a dishwasher uses cold water, while most washing machines are plumbed to both the hot and cold water pipes. Most washing machines and dishwashers will work with their inlet hoses temporarily attached to the hot and cold (or only the cold) taps and with an emptying hose hooked over the edge of a sink. However, they are much better to be permanently plumbed in as temporary tap fixings are more likely to leak and their use means that sink taps are 'out-of-action' until the laundry or washing-up has been done.

When you fix a machine permanently, the hoses still give enough length for the machine to be moved around 30cm 1ft, allowing you to clean around and behind it. The machine's vibrations would soon cause rigid pipes to break or joints to leak. The instructions supplied by the manufacturer with your machine should tell you what water pressure is required for it to operate efficiently and safely.

The storage cistern must be high enough to provide the right pressure. Where 15mm (1/2in) hot and cold water pipes run conveniently behind it next to the machine, you can use a valve, which bores a hole in the pipe without having to turn off the supply and drain the system. The valves are colour-coded for hot and cold and each has a threaded outlet to fit a standard machine hose.

If you have to run a branch pipe, turn off the water and drain the system. Take branch pipes from the hot and cold pipes (or cold only) supplying the kitchen taps. Run the pipes close to where the machine is to be located and fit a small appliance valve - either an in-line, right angle or tee-piece valve, whichever is the most practical to connect to the plumbing - with a standard compression joint for connecting to the pipework and a threaded outlet for the hose.

These small appliance valves are invaluable because you can turn off the water to service the washing machine or dishwasher without turning off the water supply to the rest of the house. Connect the blue machine hose to the cold supply and the red hose to the hot.

Washing machines and dishwashers are supplied with an outlet hose, which must be connected to a waste system to discharge dirty water into a yard gully or single waste stack. The standard method uses a vertical 43mm (1 1/2in) plastic standpipe attached to a deep seal trap. The machine hose fits into the open-ended pipe to avoid siphoning back dirty water. Run the wastepipe through the wall into the yard gully or attach it to the drain stack with a strap boss and allow a fall of 6mm (1/4in) for every 300mm (1ft) of pipe run.


You will only be able to repair minor faults to washing machines and dishwashers. Some of the most common problems are:

  • No power, or intermittent power: Check the plug fuse and connections, or main fuse box. If these are intact, then the fault is most likely with the motor or there is a fault in the electrical system.
  • Water leaks: Tighten the hose connector if it has come loose. A split hose or leak due to a fault within the machine can cause serious flooding, so fit an overflow safety valve onto the supply.This measures the amount of water passing through it. If a fault occurs and the volume of water exceeds the predetermined limit, the valve shuts off the water supply to the machine. Setting instructions are provided by the manufacturer to allow for the capacity of the machine. You may also need to clean or replace the filter in the supply pipes.
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