Re: Cold fill and energy.
The miniscule amount of water now used for the wash cycle would mean in an average house the distance of the washer from the boiler would mean that the hot water would be unlikely to reach the washer and get left in the pipes,ie like running the tap waiting for the hot water to appear.
Think we were always told that warm/hot water tends to set stains on clothes as opposed to starting the wash with cold water.
Probably the vast majority of households on the old header tank for hot which produces a problem with back pressure from the cold supply when mixed although would presume this device prevents that.Mixer valves on the
American top loaders,with mixer valves sometimes suffer from that although just thought it would probably be worth it for the water guzzlers perhaps,they usually end up washing more in cold or just of cold.