The Technology Connections guy on YouTube thinks so

It is real.

Here's the biggest rabbit hole you can go down. Alec has multiple videos just about dishwashers.

https://youtu.be/jHP942Livy0

You can curse me later when you've spent 2 hours learning about Christmas light colours and LEDs.

The technology connections guy says it helps assuming your dishwasher water connection is at the sink and that the heating element in your washer isn't very good or efficient.

Detergent packs are kinda wishy-washy (Dishwashers Explained)

Yes, as many others have said, there is an explanation for running the hot water before turning on the dishwasher.

However, your partner is wrong. The purpose of running hot water is to prime the hot water pipes. Once that's done you can go ahead and wash your hands with cold water, because the hot water pipe is already full of hot water.

It's correct if in a country where the dishwasher lacks its own water heater.

Dishwashers in the U.S don't have water heaters and therefore it's beneficial to purge lukewarm water from the hot water line before starting the dishwasher, such that the water in the dishwasher is on average hotter and as such more effective at washing the dishes.

Dishwashers in Europe have water heaters and as such it's entirely irrelevant to do it there

This is primarily a North American concern. A 15amp 120V circuit does not heat water fast enough for the pre-wash cycle to actually have hot water in it. The wash cycle will eventually get hot water but not until at least halfway through, so for half of it you're washing with cold/warm water at best. Depending on what you're washing, that may be okay, but the dishwasher will definitely wash better if it is connected to the hot water supply and the hot water pipe is pre-filled with hot water by running the tap at the sink. European dishwashers are often connected to cold, because they have 220V+ heating elements that can deliver a lot more heat energy and they are designed for this. North American dishwashers are not.

The drain does not matter, you can pour whatever you want down the drain. The concern is on the supply-side only, and only applies if the dishwasher is in fact connected to the hot water line (which it should be, in North American installations, but sometimes it is installed wrong)

I believe one of the technology connections videos talks about making sure the sink water is hot so the dishwasher can have hot water and not clean with cold water

It might be this video
https://www.youtube.com/watch?v=jHP942Livy0

https://m.youtube.com/watch?v=jHP942Livy0

Here is a video from someone explaining why you should run the water hot before turning on the dishwasher, along with a few other tips.

Yes. For a typical American dishwasher installation, anyway, where the dishwasher is connected to the hot water line which is in turn connected to your storage tank water heater.

First, your water heater is already full of hot water that you've already paid the energy cost to heat up. It's therefore nonsensical to deliberately pump cold water from the line into your dishwasher only for the dishwasher to have to heat it up (using energy/money) and then have your water heater also heat up the displaced water inside it that was just pumped out.

On dumb dishwashers that don't do anything to sense the internal water temperature, this will also moderately improve your wash performance. (GE calls this feature "Automatic HotStart," for instance. Other brands call it something different. These machines will pause and run their little internal water heater coil at full blast until their current charge of water is at a temperature their programming considers acceptable to start the cycle. There is no performance detriment in this case, but it will cost you time and more energy/money.)

Modern dishwashers use a surprisingly small amount of water per cycle. Usually somewhere around 3.5 gallons for the entire thing from start to finish. This is contrary to what your parents think, who will insist to you they can totally hand wash an entire sink of dishes with "less water" than that wasteful dishwasher, which they absolutely cannot. Your dishwasher is not consuming water the entire time it is running. It will fill and recirculate that fill's worth of water inside itself, usually going through 3 or 4 phases of filling and draining throughout the cycle to arrive that that final water usage figure of around three and a half gallons. Therefore it does not readily have access to hot water unless you've primed it by running your sink, as what used to be hot water in your pipes rapidly cools off when said water is not flowing. Your dishwasher probably will not draw in enough water in one fill cycle to purge all of the standing cold water that's in the pipe unless the distance from your water heater to the dishwasher is unrealistically short.

(The latter actually is the case for the dishwasher at my office, which is fed by an undersink "low boy" water heater that's directly next to it and only separated from the dishwasher by a grand total of about 18 inches of pipe.)

Yes. Foolishly most of the less expensive dishwashers don't heat the water themselves, and the first cycle is more effective if it doesn't have a period of using cool water from the pipes until the hot water arrives.

I was skeptical at first too but it truly works.

But it may be worth clarifying to your partner that once the water is coming out of the tap hot, the water in the hot pipes is already hot, so turning the tap to cool at that point no longer negatively impacts the dishwasher.

The important part is getting the cool water in the hot water pipes that has been sitting there flushed out before starting the dishwasher. If that's already achieved, then what you do with the tap doesn't matter anymore

Is this an American thing? Dishwashers run off the cold water and heat it up themselves over here.

Depends on how the dishwasher is connected, but I would assume it's connected to the cold water. At least that's the common way in Scandinavia

Edit: okeedokee I'm wrong.

GE Appliances: Dishwasher - Correct Water Temperature

Ummm...what are all the USA people in here talking about?

I've installed and replaced my own dishwashers 4 or 5 times over the years and helped friends and family members many times. They only last about 5-7 years so it happens often enough for it to be routine for me.

The water supply is connected to the cold water. The dishwasher has it's own heating element. It heats the water to "sanitizing" levels. There's even a sanitize button.

That water gets so hot that I can't open the door mid-cycle with my reading glasses or they'll get completely fogged up.

The sanitize button is not a new development...

Yes, hot water cleans better, and results in dryer dishes due to condensation drying.

The heating element in a dishwasher is weak. It can’t heat water up that well since it’s limited to 120v and probably not even 20A. The first rinse cycle will effectively be cold water.

Your tank water heater is 240v and has a dedicated circuit, probably 30A. It can heat a lot of water, fast.

If you’re concerned about wasting water you can get a small tank or tankless hot water heater under the sink. Your water will then be hot nearly always.

Some wash cycles will both purge more water and heat it up longer to compensate.

Technology Connections (youtube channel) says yes run until it's hot IF you have trouble with dirty dishes, iirc. I think the bigger thing is to clean your debris trap. Also you should be fine washing your hands. The dishwasher will still pull as much hot water as it needs, they are typically only hooked up to hot water so it's not like you having the tap on mixes it up or anything.

Your dishwasher uses hot water so if you run your sink until hot water is coming out before running your dishwasher it means it's immediately getting hot water. It's about clearing the cold water out of your pipe.

Whether or not you can use the sink while the dishes are being washed depends on your water heater. If you can wash your hands while someone is taking a shower without blasting them with cold water then you should be fine to use your sink while the dishes are being washed.

Maybe take a look under your sink and check if the dishwasher is connected to the cold or warm water line. It only matters if it is connected to the warm line.

In the United States and other countries with 120V electricity

My sibling’s dishes won’t get clean unless she runs the water first, as her sink takes a crazy amount of time to warm up.

YMMV though. Not all sink piping takes so long to “warm up” anyway.

So test it!

Run a dirty load. If your dishes get clean in the dishwasher, no problem; your routine ain’t broke. If you aren’t satisfied, try running the hot water first.

It’s certainly not worth an argument with an SO though, as it could plausibly help.

The dishwasher has a heating element inside and it's using maybe 4-5L max for the wash cycle. It heats up pretty fast.

I’m not sure why you’re being chastised for using water while the dishwasher is filling. That is a non sequitur. But for most people, the answer is probably yes, it moderately improves performance.