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Can I use a cold water line for my Bosch dishwasher?

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  • Sep 1st, 2021 1:48 pm
[OP]
Member
Dec 29, 2019
266 posts
139 upvotes
Toronto, Ontario

Can I use a cold water line for my Bosch dishwasher?

A few months ago I ordered a Bosch Benchmark 24" dishwasher: https://www.bosch-home.ca/en/productlis ... ab-4357071

It's backordered to hell so I probably won't be receiving it until October or November, but in the meantime I am trying to make sure I can install it properly.

My house is still under renovations, but when I asked to have dishwasher and sink water lines added to my island, they put two cold (blue) and one hot (red).

I am reading the installation guide and it says it should use a hot water line. However, on this FAQ page for Bosch, it says they prefer a cold water line to be used gor all their machines:
https://www.bosch-home.co.uk/customer-s ... /hot-water

I emailed customer support and they said to ignore the info because it's from the UK/euro site and use the hot water line.

The dishwasher itself does have water heating capacity, and I imagine maybe there is not two different dishwashers but who knows..

So can I save myself the trouble and just input cold water and wait the few extra minutes it would take to heat up or would that really be bad?
17 replies
Deal Addict
Sep 13, 2016
3441 posts
2219 upvotes
Mississauga
You can install a T valve to add one more outlet for your hot water connection and feed both your tap as well as dishwasher.
[OP]
Member
Dec 29, 2019
266 posts
139 upvotes
Toronto, Ontario
IndyBeak wrote: You can install a T valve to add one more outlet for your hot water connection and feed both your tap as well as dishwasher.
Yeah, I know that is one solution, although I wanted to know if it was possible or damaging to the machine to use cold water anyway.

Plus, do I just leave my other cold water line to live in obscurity? lol
Deal Addict
User avatar
Oct 9, 2010
3121 posts
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Windsor
Meibatsu wrote: Yeah, I know that is one solution, although I wanted to know if it was possible or damaging to the machine to use cold water anyway.

Plus, do I just leave my other cold water line to live in obscurity? lol
Does your house have a spare spot on the hot water manifold? If so, just move one of the cold water lines to the hot water manifold at the source end. Just because it's blue, doesn't mean it can't have hot water in it. Wrap the end in red tape if you really want to show that it's supposed to be red.
One who is offended by truth, has no place among those who seek wisdom.
[OP]
Member
Dec 29, 2019
266 posts
139 upvotes
Toronto, Ontario
ChubChub wrote: Does your house have a spare spot on the hot water manifold? If so, just move one of the cold water lines to the hot water manifold at the source end. Just because it's blue, doesn't mean it can't have hot water in it. Wrap the end in red tape if you really want to show that it's supposed to be red.
I am not sure. I would have to check but am wondering how much a hassle it would be to "reassign" as the lines came out of a small hole in the floor and are now surrounded by cabinet as well.
Deal Addict
User avatar
Oct 9, 2010
3121 posts
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Windsor
Yeah,bdont change it at the cabinet side, change it at the manifold if you have one. If it's not home-runs, and just tees, then you would have to change it in the cabinet.
One who is offended by truth, has no place among those who seek wisdom.
Deal Guru
Sep 2, 2008
12435 posts
2179 upvotes
First thing should be to ask who installed the lines what's up. It's probably not hard to fix, or just T off the hot line and cap the extra cold line.
Newbie
Dec 4, 2018
18 posts
14 upvotes
Your plumbers didn't mess up. Standard practice is to use a tee off your hot line to service a dishwasher. One hot and two cold supply lines is preferred. One cold is for your sink, the other is reserved for a drinking water filter (RO or carbon, for example).

Your first cold line may be soft water while the second is hard for taste. Check this as well.
[OP]
Member
Dec 29, 2019
266 posts
139 upvotes
Toronto, Ontario
JMKRFD wrote: Your plumbers didn't mess up. Standard practice is to use a tee off your hot line to service a dishwasher. One hot and two cold supply lines is preferred. One cold is for your sink, the other is reserved for a drinking water filter (RO or carbon, for example).

Your first cold line may be soft water while the second is hard for taste. Check this as well.
Oh! Makes sense if I was supposed to tee off the entire time.

How will I be able to tell if a line is hard or soft water? I don't think I have a water softener so.. lol I am in Toronto if that makes a difference.


But also I am still in search of my answer of whether theroectically I can just use cold water for my dishwasher without harm.
Deal Fanatic
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Oct 12, 2007
7821 posts
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Ottawa
To the original question: these new dw's do have in-line heaters but they are made to boost the intake water temperature, not to heat it from cold. If you don't use hot water as your dw supply line, you run the risk of prematurely burning out the dw heater. Plus, you're heating the water with electricity (vs NG for many homes) so the expense goes up. In fact, I run the kitchen sink hot water faucet until it's hot to the touch before I turn on my dw as that increases the amount of truly hot water that gets to the dw (as opposed to whatever the temperature of the water is after sitting in the pipes).

Re. the softener: If you don't have a water softener, none of your lines are softened. You should start with looking at what comes into the house and trace it forward. Mine (for example) comes in from a well, goes through a 3 stage filter and then splits into two with one going to a water softener. The other (unsoftened) line feeds the cold water at the fridge, all sink faucets, toilets, and the outdoor house bibbs; the other goes through the softener and that feeds the hot water tank (ergo anything hot is softened) as well as the washing machine, showers, laundry tub, and bath tub. I designed the system myself when we did a whole-house reno and I pity the next owner of the house trying to figure out the system - if they're not handy.
Deal Fanatic
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Oct 15, 2007
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Some Bosch dishwasher require cold but some do still require hot. If yours requests hot (which is standard) then hook up to hot only. Tee off the hot line under your sink (like any other dishwasher would)
The second cold line is likely a supply loop for a fridge or a pot filler, or a hose bib. Etc. So it can be isolated under the sink.
Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide
Newbie
Dec 4, 2018
18 posts
14 upvotes
To confirm requirements for the original hookup, the installation manual further down on the product page you linked above (Canadian, not UK) says to hook it up to the hot water line. You'll want to do that for the reasons mentioned above.

And regarding soft water, if you can't trace the line back to a softener you likely don't have one. However hardness testing strips commonly available from any pool store would confirm this.

Might be a good time to put one in if you're currently undergoing a reno.
Deal Addict
Mar 3, 2009
1624 posts
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Ottawa, ON
As per the installation manual:
The hot water heater should be set to deliver approximately 120° F (49° C)
water to the dishwasher. Water that is too hot can cause some detergents
to lose effectiveness. Lower water temperatures will increase run times. The
hot water supply pressure must be between 15 - 145 psi (1 - 10 bar).
So it does need a hot water supply running to it. I can understand your confusion though as UK / EU dishwashers often take cold water and heat it but in North America I've only ever seen a hot water line ran to a dishwasher.
Deal Addict
Nov 27, 2013
1597 posts
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CaptSmethwick wrote: In fact, I run the kitchen sink hot water faucet until it's hot to the touch before I turn on my dw as that increases the amount of truly hot water that gets to the dw (as opposed to whatever the temperature of the water is after sitting in the pipes).
Never thought of that. Good tip.

With the amount of time it takes for water to get hot in the morning i suspect the dishwasher would be almost completely filled with room temp water.
Deal Addict
May 21, 2015
1202 posts
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Sarnia, ON
THe reason why UK, euro machines , dishwashers and washing machines use cold water is because they operate on roughly 220 volts and are quite capable of heating the water fast.
Deal Fanatic
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Oct 12, 2007
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Ottawa
Also, water that is supplied too hot can (a) damage the internals of some dw's; or (b) adversely affect their performance. I have also read that cooler (but still warm-to-hot) is better for the crystal cycle (if the dw has one). Most North American homes have temperature regulators for their hot water. If your temperature at the tap is 50 degrees Celsius or less, a hot water hook-up is usually what is required; if the tap water temp is much higher than that, you might want to call the dw manufacturer's no-help line. I find the Miele people to be very helpful but all other manufacturers significantly less so.
[OP]
Member
Dec 29, 2019
266 posts
139 upvotes
Toronto, Ontario
CaptSmethwick wrote: Also, water that is supplied too hot can (a) damage the internals of some dw's; or (b) adversely affect their performance. I have also read that cooler (but still warm-to-hot) is better for the crystal cycle (if the dw has one). Most North American homes have temperature regulators for their hot water. If your temperature at the tap is 50 degrees Celsius or less, a hot water hook-up is usually what is required; if the tap water temp is much higher than that, you might want to call the dw manufacturer's no-help line. I find the Miele people to be very helpful but all other manufacturers significantly less so.
I have a Rinnai tankless that I think will allow me to control the temperature of the water, so hopefully too hot won't be an issue!
Deal Addict
Jul 2, 2006
1578 posts
830 upvotes
Toronto
CaptSmethwick wrote: Also, water that is supplied too hot can (a) damage the internals of some dw's; or (b) adversely affect their performance. I have also read that cooler (but still warm-to-hot) is better for the crystal cycle (if the dw has one). Most North American homes have temperature regulators for their hot water. If your temperature at the tap is 50 degrees Celsius or less, a hot water hook-up is usually what is required; if the tap water temp is much higher than that, you might want to call the dw manufacturer's no-help line. I find the Miele people to be very helpful but all other manufacturers significantly less so.
Meibatsu wrote:
I have a Rinnai tankless that I think will allow me to control the temperature of the water, so hopefully too hot won't be an issue!
Bosch wash cycles are typically within 50-70 Celsius (120-160f) and the max you can really go on the Rinnai is 60 Celsius (140f) (that's after you override the safety jumpers in the machine). You can likely only adjust up to 120f on the Rinnai so I wouldn't even consider water temp as a risk factor.

Yes - the correct way is to T off the hot water supply line to feed the dishwasher.

Source: I own both a Rinnai tankless and a bosch dishwasher.

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