Since dishwashers always use really hot water, why are they routinely attached to the cold water supply?

Dishwashers work best when fed with cold water.

The reason is, some foodstuffs are cleaned off better with cold water, such as egg, which would get baked on by hot water.

Modern machines fill with cold and then heat the water themselves, this way you get the benefit of cleaning at all temperatures as the water temperature slowly rises.

Also they rinse in cold water, it would be a waste of hot water for this.

Also in many houses it takes some time for the hot water to reach the machine, test this by turning on the hot tap and see how long it takes for the water to get hot, since modern machines use a very small amount of water the hot would often not reach the machine by the time it had finished filling.

OK, first of all now days most dish washers are hooked to cold water taps because they heat the water to their preferred temperature. Those "plumbers" that have not heard of this apparently haven't read any instruction manuals for a while.

The solar panels do not supply an unending supply of hot water like your gas or electric water heater, so the solar guys want to use a mixing valve to reduce the temperature of the water to the temperature the dishwasher requires and not waste a lot of solar supplied water in the process.

Running something like a dishwasher which uses a lot of hot water will very quickly deplete all the hot water from the solar panels. If this is done after the sun has gone down for the day, you will have no hot water until the next day.

What the heck is a "gubbins"!

The heater in a dishwasher sets the water to a very accurate temperature that is not guaranteed from the house hot water system.

The machine also uses cold water if its set to certain rinse cycles. If it was connected to the Hot water only then that would be wasting your house hot water supply.

Compared to a conventional gas/electric boiler and storage system the internal machine heater actually costs less because it's only heating the water that you use. Remember that the first 3 litres of water coming from the 'hot' tap is probaby cold anyway - and the last 3 litres of hot water left in the pipe is hot (and cooling) so all that's wasted money.

Your solar panel won't respond fast enough for the dishwasher demand.

All of the above applies to most modern washing machines too.

When I bought my dishwasher and had it installed the plumber asked me if I wanted it connected to hot or cold water. Apparently the dishwasher has its own heater and washes dishes at a temperature of approximately 60 to 70 degrees. He told me it's fine to hook up to cold water (so as not to use up all the hot water). However my dishwasher has no option to say 'heat'; it just heats automatically (I think it heats less, e.g. only 50 degrees when I choose 'eco' option). I've never had a problem with it hooked up to the cold. NB This was in Melbourne, Australia (I don't know about other places)

It's maybe an American thing where the hose is attached to the hot water pipe, mine was plumbed in using cold water and like you wondered why. Don't think the shower issue would be a problem because most electric showers are plumbed in using a cold water supply unless you are running it off a combi boiler system, and unless your water pressure was really low you shouldn't have a prob. I'd ask an independent plumber (or two in case you get a Big type of guy...) before splashing out on something that may be totally unnecessary.

I can not explain why they are hooked to the cold water line.I also wondered the same thing about twenty years ago, and hooked up my dishwasher to the hot water line.

I didn't really see a savings, OF COURSE I really wasn't looking back then, but the dishes seemed to always come out clean,as they were spending more time in hot water. And the dishwasher has not suffered any ill effects. So I would say go ahead and hook it to the hot.

i have never seen or had a dishwasher that has been hooked up to the cold water side. that is just and simply a mistake to do so. any plumber who suggest otherwise and also try to sell you a mixer, you should send home without pay. granted, your dishwasher has a build in heater and should be used only as a back up. turn it off and keep it off. again, hook up your dishwasher directly to the hot water line.

as far as your washing mashine goes just leave it the way it is hooked up. one cold line inn and one hot line inn. it does not matter if you have a solar heater or not. on your washer you have a selector switch where you can choose the water temp you want to use. the machine will mix the water automatically. just keep both hoses where they are and do not add anything else to it.

i had a solar heater for many years and it sound like to me that your plumber is looking for some extra income for him and some needless expenses for you.

this issue appeared and there is no reason why you cannot connect hot water supply if its regulated.

the reason why some dishwasher manufacturers insist on cold supply is to regulate the temperature of the supply they do not want the dishes or the machine to be damaged.

say the hot water coming in was at 60c and the wash you wanted to do was 30c or less by using hot water at 60c it will not give the same results

but it is possible check with the manufacturer ring up the customer services most manuals say cold feed only you can use hot if its regulated

and you can use one thermostatic cartridge to control whole house temperature as you can get TMV valves that would be able to do that you would not require individual ones (TMV thermostatic mixer valves)

Dishwashers use lots of water.They are connected to the cold water line because they have a heater in the bottom of the unit that raises the temperature to the desired setting. If they were to be connected directly to the hot water line it would deplete the available hot water to the rest of the house.With the dishwasher connected to the cold line you can still take a shower and not worry about running out of hot water.

I m not an expert, but I wonder if we are seeing a difference here between US & UK systems? In the UK our machines are always either cold only or I have seen washing machines that take both. They are plumbed to cold so they can internally regulate the temperature from cold to whatever the heater can manage, as has been stated by others. Most of the "it should always be hot" answers appear to be from the USA?