In general, modern washer machines have a plumbing configuration that allows for separate cold and hot water hook-ups. The hot and cold water lines connect to the washer via a valve on the back of the machine. This valve is controlled by the temperature control on the front of the washer. However, some older washer machine models do contain an internal heater to provide the washer with hot water.
The heater on older models can be located in either the rear of the washer behind the back panel or behind the front panel of the machine, beneath the door seal to the washer's tub. The heating coil element that heats the water sits in a space made between the inner and outermost rings of the main washing tub. The heater is normally secured by a bolt, a metal plate and a large piece of rubber that also provides a watertight seal so that the components of the heater do not get wet. Water is then pumped into the main tub and fills the space occupied by the heating coil. The coil heats the water, which is then used to wash the clothes. In the dual water supply system found in modern washers, if the cold water temperature control is selected, then only the cold water valve opens. If the hot water temperature control is selected, then only the hot water valve opens. If warm is selected, then both valves open for cold and hot water.