AFAIK dishwashers all internally heat the water. The machines tell you to hook up to the hot line in the US (I've heard they say to use the cold line in Europe but I don't live there), but the chance of actually getting hot water from your line is pretty minimal because they only fill for a few seconds at a time.
Maybe because our how water systems are more various, so you can't just assume that's always hot on demand when you want it? If you need a heating element in the dishwasher anyway it's not much of a feature.
I think it's: 1) might not be on-demand, so then your hot fill might not be hot at the right time; 2) if it is hot, it will almost certainly be <70C, which is typically the max cycle temp.. so you either can't have that or still need a local element to get it there; 3) even if it's hot enough, you also need cold fill, so you can mix and get the temperature(s) you need.
Frankly I think even with some assumptions about your market to ignore 1 & 2, 3 alone makes it more complex than just taking a cold fill and heating to temp within the dishwasher. I believe the very few models that do have a hot fill do it on an eco basis (you already have hot water use it here too) but the validity of that is disputed, and really the only obvious benefit is to the EPC sticker (characterising energy performance) which will appear best in class (the class of all dishwashers) just by not having a multiple kW heater, not accounting for that having been offloaded to the boiler.
Just run the tap at the kitchen sink until the water gets as hot as possible, then start the dishwasher. It'll get nice hot water straight from the pipe that way!
This works well unless you have a tankless water heater. Those are very bad for any appliances that fill water in short bursts, because they only heat while the water is flowing and the water only flows for a short time.
Yeah I am a big fan of giant tank water heaters. You can even set them up to run at the time of day when energy costs are lowest, if you have variable pricing, and the hot water will stay hot for a day or two unless you use a lot. Often energy prices will be lowest on the weekend which works great if you time your laundry cycles on those days!
You can also get small tanked or tankless water heaters that fit under your kitchen cabinet, and can help provide that hot water to your dishwasher. Which is especially important if your hot water heater is located far away from the kitchen and it would take a long time for actual hot water to arrive at your sink.
I would recommend that you look at them closely and get the one that fits your use case the best.
CR can also help here, because they will test them independently of the dishwasher.
Doesn't it fill several times, with long periods of time in between? If so, this trick (which I do use, personally, in spite of this criticism) only benefits the first of several fills. Better than none, though.
According to the Technology Connections video (linked several times in this discussion, including by me), dishwashers usually use their internal heating element to heat the water during the main cycle. The reason for running the tap is just to make sure the water is hot during the prewash cycle, since the dishwasher does not use its heater for that one (since the time is so short)
