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Old 01-13-2019, 08:12 PM
Jinx Jinx is offline
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Plumbers: Does A Dishwasher Need a Hot Water Line?

My Whirlpool dishwasher's manual says the incoming water should be at 120 F. But, from what I understand, dishwashers connect to a cold water line. What's the story here? (My main concern is that the dishwasher is no longer getting hot enough to clean the dishes. I do have hard water, and I wonder if the heating element is reduced in effectiveness or damaged. We have tried running the dishwasher empty with two cups of vinegar placed in the bottom rack, as the manual suggests. Also, we are trying to run the dishwasher empty with some citric acid in it - a recommended home remedy.) The dishwasher is four years old now. This issue of not cleaning [and not drying (even with Jet Dry)] has started in the last week or two. We believe the dishwashing soap (detergent) is opening at the right time.

Comments? Thoughts?

Last edited by Jinx; 01-13-2019 at 08:13 PM.
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Old 01-13-2019, 08:25 PM
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Not a plumber, but where are you?

In the United States at least, dishwashers are hooked to the hot water only. There is no cold water connection. I understand this is different elsewhere.

This Old House:
Quote:
Though traditionally dishwashers get hooked up to the hot-water supply, you can save even more energy by connecting to the cold water because the heating element in the dishwasher uses less power than a water heater. However, check manufacturers' literatureósome companies' models must be supplied with hot water.
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Old 01-13-2019, 08:25 PM
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I have never, ever seen a dishwasher connected to a cold water line.

My recollection is that 35 C (95 F) is the optimal temperature for dishwasher water, although newer ones do have built-in preheaters.

Last edited by Leaffan; 01-13-2019 at 08:26 PM.
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Old 01-14-2019, 04:47 AM
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My dishwasher, a Miele, connects to the cold water line. I'm in the UK.
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Old 01-14-2019, 04:49 AM
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My dishwasher, a Miele, connects to the cold water line. I'm in the UK.
That's crazy.
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Old 01-14-2019, 05:10 AM
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Originally Posted by Quartz View Post
My dishwasher, a Miele, connects to the cold water line. I'm in the UK.
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Originally Posted by Leaffan View Post
That's crazy.
Not crazy, just not done the same way as in the States.
There's a heater in the dishwasher.
I'm not sure about our dishwasher, but the clothes washer in our place is hooked to the cold water line. This is in Australia. When I want hotter wash water than tap temperature, which isn't often, there's a heater in the washer for that. That way, it heats no more than it needs to.
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Old 01-14-2019, 05:17 AM
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Sorry for the double post, but I just hunted up the installation manual for our dishwasher.
It recommends connection to a cold water line, and says that hot water connection is optional, but only under certain conditions (max temp, pressure, etc).
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Old 01-14-2019, 08:42 AM
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Originally Posted by Jinx View Post
My Whirlpool dishwasher's manual says the incoming water should be at 120 F. But, from what I understand, dishwashers connect to a cold water line. What's the story here? (My main concern is that the dishwasher is no longer getting hot enough to clean the dishes. I do have hard water, and I wonder if the heating element is reduced in effectiveness or damaged. We have tried running the dishwasher empty with two cups of vinegar placed in the bottom rack, as the manual suggests. Also, we are trying to run the dishwasher empty with some citric acid in it - a recommended home remedy.) The dishwasher is four years old now. This issue of not cleaning [and not drying (even with Jet Dry)] has started in the last week or two. We believe the dishwashing soap (detergent) is opening at the right time.

Comments? Thoughts?
I believe, but could be wrong, that hard water causes issues with heating elements when the element is so covered in deposits from the water that it's effectively insulated. You'd be able to see that. If you ever drain a water heater, often times you'll find chunks of stuff coming out with the water. When all that sediment fills up the bottom foot or so of the heater it can making it harder for the gas burner to get heat into the tank or cover the lower heater in the case of an electric water heater.

Running vinegar may help clean the inside of the dishwasher and/or the pump, but I don't think it's going to help with your heating issue.

If you think your heater isn't working, you could try opening the dishwasher 20 or 30 minutes after it's started and see if expected cloud of steam comes billowing out or if the water is cold/colder than expected. If the water is cold, it may be an issue with the heating element, the wiring, the circuitry or relays that control it or something else.
However, the easiest fix is likely going to be to simply move the connecting to the hot water side.
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Old 01-14-2019, 09:26 AM
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What's the model of the washer? Does it have a filter that may need to be cleaned? Have you checked the manual for troubleshooting tips?

If it worked find for 4 years and then stopped working fine, I'm inclined to believe something changed (as opposed to getting gradually worse). Maybe the heater did break. Is someone different loading it? If it's being loaded differently (or incorrectly) because of who's doing it, that could cause issues. I've seen at least 2 cases where one person always loaded it, then one day a different member of the household did it and didn't realize, for example, that having a big bowl on the bottom rack in just the wrong place prevented the top rack from getting sprayed. The other person, knowingly or not, never put anything there.

TL;DR
What's the model?
Any change in who or how it's loaded?
Check the manual.
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Old 01-14-2019, 10:58 AM
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Read the owner's manual, it could be either hot or cold. I believe many in the US connects to hot. The reason seems to be time savings, and perhaps our 110V standard, while Europe is more energy consciences and have 220V to play with as their standard - so they can heat that water faster, plus from what I've seen many of their appliances take longer then we are used to in the US.
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Old 01-14-2019, 11:18 AM
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Originally Posted by Jinx View Post
This issue of not cleaning [and not drying (even with Jet Dry)] has started in the last week or two.
Other people have commented on the hot/cold thing (I'm in the UK, my dishwasher connects to cold and heats it up), but if I hear about a dishwasher that suddenly loses cleaning efficacy, I think the spray arms aren't going around, either at all or not as fast as the should. They could be blocked - it's worth seeing if you can get them off (in mine it's a simple unscrew of a knurled nut) and then rinsing them through.
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Old 01-14-2019, 11:35 AM
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My Kitchenaid dishwasher manual says that it requires a connection to a hot water supply line at 120F at the dishwasher.

Mine is connected to a hot water line, but there is no way the water gets anywhere near that temp, as the kitchen sink takes about a minute before the hot water begins to feel lukewarm. Actually, let me just check to see what temp the water is when I run the dishwasher.

*tip toes off*

Looks like after filling, the water in my dishwasher is 70F. My water out of my cold tap in the kitchen is 64F. The dishwasher still ends up cleaning properly. I know I could let the hot water run until it does finally get hot, but I've never bothered. I suppose I could possibly/probably be eating into the lifetime of the heating element; I've only had this dishwasher for two and a half years now, but no problems with the heating element yet.
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Old 01-14-2019, 11:38 AM
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Originally Posted by Leaffan View Post
That's crazy.
Why would that be crazy? There's a heating element in the dishwasher, there's a thermostat, and apparently it's more efficient to heat the water in the dishwasher, anyway, so why would it matter if the incoming water is hot or cold if the unit is designed to accomodate cold water. It sounds like it would be better to use cold water, though perhaps slightly slower.

Last edited by pulykamell; 01-14-2019 at 11:39 AM.
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Old 01-14-2019, 11:45 AM
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Originally Posted by pulykamell View Post
My Kitchenaid dishwasher manual says that it requires a connection to a hot water supply line at 120F at the dishwasher.

Mine is connected to a hot water line, but there is no way the water gets anywhere near that temp, as the kitchen sink takes about a minute before the hot water begins to feel lukewarm. Actually, let me just check to see what temp the water is when I run the dishwasher.

*tip toes off*

Looks like after filling, the water in my dishwasher is 70F. My water out of my cold tap in the kitchen is 64F. The dishwasher still ends up cleaning properly. I know I could let the hot water run until it does finally get hot, but I've never bothered. I suppose I could possibly/probably be eating into the lifetime of the heating element; I've only had this dishwasher for two and a half years now, but no problems with the heating element yet.
I always run the hot water at the sink until I can feel hot (or at least) warm water coming from the tap before turning on the dishwasher for just that reason. I'd be willing to bet the manual for your dishwasher suggests you do that as well, especially if it wants 120 degree water.
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Old 01-14-2019, 12:14 PM
pulykamell pulykamell is online now
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Originally Posted by Joey P View Post
I always run the hot water at the sink until I can feel hot (or at least) warm water coming from the tap before turning on the dishwasher for just that reason. I'd be willing to bet the manual for your dishwasher suggests you do that as well, especially if it wants 120 degree water.
Well, I'll push my luck and be the guinea pig to let y'all know when the dishwasher heating element finally gives up the ghost. Keep this page bookmarked! (I also don't like running the water needlessly, as I have a water efficient model, so doing that kind of kills that efficiency. Like I seriously would have to run the water on my kitchen tap for over a minute to get it to 120F, unless the hot water had been run recently there before. When I need hot water for a pot, I go to the bathroom tub which almost instantly produces hot water.)

Last edited by pulykamell; 01-14-2019 at 12:18 PM.
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Old 01-14-2019, 12:14 PM
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Mine's a 5 year old Maytag, and it says in the manual that it likes the incoming water temp at 120 for optimum operation.

That said, our water heater recently went out, and it ran just fine getting tap cold water (probably 55 or so) because it also has an inbuilt heater that heated the incoming water up to the requisite temperature anyway.
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Old 01-14-2019, 12:18 PM
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Originally Posted by pulykamell View Post
Well, I'll push my luck and be the guinea pig to let y'all know when the dishwasher heating element finally gives up the ghost. Keep this page bookmarked! (I also don't like running the water needlessly, as I have a water efficient model, so doing that kind of kills that efficiency. Like I seriously would have to run the water on my kitchen tap for over a minute to get it to 120F, unless the hot water had been run recently there before.)
I'd be surprised if the element broke before something else happened that makes you replace the entire unit. Like a broken or loud motor that costs $300 to replace.
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Old 01-14-2019, 12:21 PM
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When our now 10 y.o Kitchenaid stopped cleaning effectively I broke out the manual and pulled apart the spray arms and the filter/chopper assembly which was full of goo and other bits including chunks of glass. Cleaned all that out , ran some vinegar on a sterilization cycle and she cleaned as good as new.
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Old 01-14-2019, 12:27 PM
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When our now 10 y.o Kitchenaid stopped cleaning effectively I broke out the manual and pulled apart the spray arms and the filter/chopper assembly which was full of goo and other bits including chunks of glass. Cleaned all that out , ran some vinegar on a sterilization cycle and she cleaned as good as new.
On my last dishwasher I did that regularly, whenever I noticed a problem and it always helped as well.
But as the unit got older, and louder, I eventually replaced it. I was amazed at how much cleaner everything was. Glasses that I thought were just getting etched after a decade of use came out spotless. Over the next few weeks I ran a lot of 'clean' stuff through it that I don't use often, just to get back to being spotless.
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Old 01-14-2019, 12:30 PM
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American dishwashers use household hot water. European dishwashers have integral heaters.
Now there may be the odd euro one made for the us market without a heater but I haven’t seen one.
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Old 01-14-2019, 12:43 PM
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I'd be surprised if the element broke before something else happened that makes you replace the entire unit. Like a broken or loud motor that costs $300 to replace.
Come to think of it, I did replace the motor a couple months ago. Didn't think of connecting the two. Cost me $80 to fix (I fixed it myself.) This particular model did have issues with the motor blowing out early, according to the literature I've seen online, but now I wonder if the two are connected. The only thing I see on Kitchen Aid's website is that if the water coming in isn't hot enough (because the hot water line is located far from the heater), that the loads may not wash well, but nothing about it being dangerous for the equipment.

Last edited by pulykamell; 01-14-2019 at 12:46 PM.
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Old 01-14-2019, 01:27 PM
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Originally Posted by pulykamell View Post
Come to think of it, I did replace the motor a couple months ago. Didn't think of connecting the two. Cost me $80 to fix (I fixed it myself.) This particular model did have issues with the motor blowing out early, according to the literature I've seen online, but now I wonder if the two are connected. The only thing I see on Kitchen Aid's website is that if the water coming in isn't hot enough (because the hot water line is located far from the heater), that the loads may not wash well, but nothing about it being dangerous for the equipment.
I was just suggesting that a bad motor would likely cause you to buy a new dishwasher before the element gave out. I'd be very, very surprised if they're related in any way*. Even then, I was only saying it because when my motor was getting louder and louder I checked online and the cost for a new one (motor, part only, I can fix it) was about $250-$300. Hardly worth it on such an old dishwasher, especially when I can get a brand new 'good' one for $400-$500.

*I suppose cold water could cause a seal somewhere to shrink and let water drip down in to the motor, but that's a long shot.
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Old 01-14-2019, 03:02 PM
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I was just suggesting that a bad motor would likely cause you to buy a new dishwasher before the element gave out.
Gotcha. That makes a lot more sense. Yeah, I got a little lucky with this part. I found the motor assembly for $120 at most places, but managed to get it new for $75 (plus tax) from Sears.
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Old 01-14-2019, 04:46 PM
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All the dishwashers I've had have been connected to the cold water supply. The current one (a Bosch) mentions an option to connect to the hot if you change a setting, but why would I when it has a built in heater? My hot water gets to maximum of 50 degrees Celsius anyway and the normal wash in the dishwasher is something like 60 or up to 75 degrees.

As for the OP's issue, I had much the same when the heater stopped working in my previous dishwasher. In my case, it was the circuit board of the controller, which had an under engineered track for the water heater. After a time it just burnt out because it couldn't carry the current needed.

Also, I've always been told that water heaters should store at a temperature of at least 60 degrees to prevent bacteria growth. That's 140 Fahrenheit. Do you have tempering valves to keep the temperature at the tap below 50 (120 Fahrenheit)? I have a tankless heater, so there is no storage.
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Old 01-14-2019, 05:06 PM
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This Old House, who certainly know more about house stuff than I do, say that it is more efficient to let the dishwasher heat the water than to use water from the hot water heater. Is that true? Particularly with a gas storage hot water heater compared to the electrical resistance heater in the dishwasher, I'd think the hot water heater is much more efficient at heating than the dishwasher.

I drain the cold water from the hot water pipes before starting the dishwasher, but I'm using that water to run the garbage disposal anyway, so it's not completely wasted.

I do find it odd that dishwashers and washing machines will say that the incoming hot water should be at 120F or higher, but child safety advocates will say to set it below 120F.
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Old 01-14-2019, 05:28 PM
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It's probably worth mentioning that even if the dishwasher can heat the cold water with no problem and even if it costs the same to have either one heat the water, the dishwasher manufacturer is still going to prefer hot water to come in since that puts less stress on the heating element, speeds up the cycle time by reducing how long it has to wait for water to come up to temp* and, not running the element as much means it uses less electricity. Even though you'll still pay for that energy at the water heater, the actual dishwasher will use less and the big yellow sticker on the box showing energy usage will look better.


*I don't actually know if the machine waits for the water to heat up. It probably varies from machine to machine, but it can't take more than a few minutes so the cycle might just start anyway and the heater/t-stat do their thing.
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Old 01-14-2019, 06:04 PM
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We've got some pretty damned cold groundwater here, especially in the winter. I have never seen a dishwasher here connected to a cold water line. Hell, I've installed a couple myself and didn't even know it was an option. In fact, it probably isn't.
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Old 01-14-2019, 06:15 PM
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I have a countertop dishwasher, that hooks up to the spit, set for Hot.
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Old 01-14-2019, 06:34 PM
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Quote:
Originally Posted by This Old House
Though traditionally dishwashers get hooked up to the hot-water supply, you can save even more energy by connecting to the cold water because the heating element in the dishwasher uses less power than a water heater.
Quote:
Originally Posted by pulykamell View Post
Why would that be crazy? There's a heating element in the dishwasher, there's a thermostat, and apparently it's more efficient to heat the water in the dishwasher, anyway, so why would it matter if the incoming water is hot or cold if the unit is designed to accomodate cold water.
This seems pretty questionable to me.

It's at the very least going to vary locally. The dishwasher is likely heating the water electrically, while my water heater is gas. It is definitely not going to save me money to heat up water with electricity compared to gas.

In general a resistive heating element surrounded by water is going to be as efficient as any other resistant heating element surrounded by water. Pretty close to 100% of the energy is going to go into heating the water. I guess you have lower transmission losses if you're heating the water at the dishwasher and not warming up the pipes, but again, that will only be relevant if your water heater is electric. Many are not.
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Old 01-14-2019, 08:33 PM
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Thanks for everyone's thoughts. Now, let's try a slightly different angle of attack: What is the ballpark price for a new heating element? Is it worth replacing the element or simply replace the dishwasher? (FYI: I can share our water softening system recently got a "tune-up". It was my misunderstanding thinking that the whole system can regenerate itself. This is only half-true. So, a new dishwasher will reap the benefit of the recharged softening system. I will share that, in general, I do not see scaling building up elsewhere inside the dishwasher.) Meanwhile, I will take a close look at the heating element for scaling and will verify my water supply IS from the cold water supply. ...Maybe the heating element simply burnt out.
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Old 01-15-2019, 05:48 AM
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For the dishwasher I have, the heating element is about $70, plus shipping, online from www.appliancepartspros.com (just the first site I found). The dishwasher is about $800-$1200, plus installation.

Now, unless you repair it yourself, it will probably be $250 in labor for the repairs, or more. If the heating element is what is bad, it is still obviously cheaper to repair, but if it's something with the electronics that turns on the heating element, it could easily make more sense to replace it than repair it.

BTW, I don't think hard water will harm the heating element in a dishwasher, at least the ones I am familiar with. Hard water kills the heating elements in water heaters because the scale precipitates and falls to the bottom of the tank, settling on the element. When the element gets covered with scale, it can overheat as well as suffer corrosion issues. With the dishwasher, the scale isn't going to build-up, so it sholdn't affect it. The soft water will reduce spots on the glassware, though.
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Old 01-15-2019, 07:27 PM
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Quote:
Originally Posted by pulykamell View Post
Why would that be crazy? There's a heating element in the dishwasher, there's a thermostat, and apparently it's more efficient to heat the water in the dishwasher, anyway, so why would it matter if the incoming water is hot or cold if the unit is designed to accomodate cold water. It sounds like it would be better to use cold water, though perhaps slightly slower.
For me, itís crazy because the hot water is already hot thanks to our gas water heater, and paying for the electricity to have the heating element heat it is much more expensive.
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Old 01-15-2019, 08:17 PM
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For me, itís crazy because the hot water is already hot thanks to our gas water heater, and paying for the electricity to have the heating element heat it is much more expensive.
Either way, if you're using X gallons of water heated to 60C, you have to pay to have X gallons heated up, whether it's in the washer itself, or in the hot water heater.

Diving a little more deeply...and these apply to Australia.

Quote:
Australiaís Plumbing Code dictates that hot water system temperature must be kept at no less than 60 degrees Celsius.
From here.
From the installation manual for my dishwasher:
Quote:
Hot water connection is an option, providing the supply conforms to the following conditions:
a)The maximum possible temperatrue for the hot supply is 65C. Any higher temperature may cause damage to water carrying components.
From the paper in front of me.

Now, that's a pretty narrow window - much easier to heat the water that the dishwasher needs in the dishwasher, I'd say. I'm not a plumber, true, but I can't imagine going to the extra trouble to attach a temperature tempering valve, to hook a dishwasher to hot water, when there's no good reason to do so.
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Old 01-16-2019, 03:56 AM
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Bear in mind that not everyone around the world has unlimited hot water. For me, how much hot water I have depends on how much sun I had today, as well as whether I remembered to turn on the boiler's electrical heating. In any event, I wouldn't waste hot water on a machine that can heat water itself.
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Old 01-16-2019, 01:07 PM
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My dishwasher is under the counter in kitchen next to the sink. It is connected to the sink's hot water line only. We usually run the hot water tap in the sink until hot water comes out before starting the dishwasher.

The heating element as far as I know, only comes on at the end of the wash cycle to dry the dishes.

I installed it per the directions a couple of years ago.

Last edited by Dallas Jones; 01-16-2019 at 01:08 PM.
  #36  
Old Today, 12:48 PM
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Either way, if you're using X gallons of water heated to 60C, you have to pay to have X gallons heated up, whether it's in the washer itself, or in the hot water heater.
Right, but for many people the water heater is a lower cost heater than resistive electrical heat. Not everybody, but quite a lot. Because burning something locally to make heat is a lot more efficient than burning it to heat water to spin turbines to oscillate electrons to heat up a resistor a long way away.

Quote:
Now, that's a pretty narrow window - much easier to heat the water that the dishwasher needs in the dishwasher, I'd say.
I don't think five degrees C is that narrow a window. Water heaters have a thermostat in them, so you can just set it to something between 60 and 65. Not sure that "easier" matters much. Like, both heaters are present, so you should use the lower cost one.

If all your heating is electric, then it doesn't matter. If you have some combustable source of heat, then that's almost certainly a cheaper way to heat things.
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Old Today, 03:10 PM
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Originally Posted by galen ubal View Post
Either way, if you're using X gallons of water heated to 60C, you have to pay to have X gallons heated up, whether it's in the washer itself, or in the hot water heater.
Diving off tangent for a second - I'd literally never heard of the recommendation to keep your water above 60 degrees - in fact, the last thing I'd heard on the subject was a recommendation to go as low as was practical, to save money and keep your kids from scalding themselves. So thanks for your cite - that's interesting and thought-provoking.

Back on topic, it just shows that dishwasher manufacturers can't reliably assume anything about the temperature of the water going into a machine. Who knows, in another 10 years someone may come up with a reliable method to eradicate all legionella from the environment, and then we'll be back to keeping our tanks at 45 again.
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