I’ve had several people ask if you can connect a cold fill washing machine to the hot water tap. They were unhappy about the disappearance of the hot water valve in UK washing machines.
Many people who are using solar powered energy to heat their water, or who had another cheaper environmentally friendly supply felt that the advantages of their environmentally friendly and economical hot water will be wasted by not utilising their hot water supply.
However, the answer to the question is no, for the following reasons..
Water is too hot
The incoming water temperature would be too hot (usually at least 60 degrees Centigrade). This can damage delicate laundry and shrink woollens. There would be no way of controlling the temperature of the water. A washing machine designed to use hot & cold water will control the potential temperature of the hot water by filling only with cold water on all wash cycles except the really hot wash.
Too hot for most wash cycles
The temperature of household hot water is also too high for most commonly used wash cycles, which only need 30 or 40 degrees. It is pointless putting on a wash cycle that needs to heat the water up to 30 or 40 degrees if the water is 60 degrees from the start. So apart from potentially damaging some laundry, the washing machine’s thermostat would close almost immediately and the wash cycle would move on to the rinsing too soon. This would shorten, but compromise the wash quality…
No good for biological detergent
Biological detergent contains living enzymes. The enzymes are killed off at the temperature of most people’s hot water. So wash efficiency would again be compromised when using biological detergents. This type of detergent is more effective when starting in cold water with the water gradually heating up.
Rinsing in hot water is very bad
The laundry would also be rinsed in hot water. This would cause severe creasing as well as wasting all the hot water and being very energy expensive.
You can’t swap the cold water supply for a hot supply. However, there might be an argument for using a y-piece to connect both hot and water supply at the same time. However, this seems a lot of trouble for very little benefit. You would need to manually adjust the water pressure of both supplies to get a balanced, “warm” combination. But as hot water usually takes a while to run through the pipework, the chances are it wouldn’t use much if any on the wash cycle anyway (this is in fact one of the main arguments for cold fill only machines). It would rinse in warm water, which may or may not be better. But it would use a lot more energy.
A full explanation as to why almost every washing machine is cold fill these days is here – Pros and cons of hot and cold fill verses cold fill washers