dishwasher plumbing dilemma

Does anyone know if the dishwasher should be connected to the hot or cold (or both pipes) pipes?

Today, a plumber installed my dishwasher to what he says is the cold tap (Blue symbol on tap nut)...however, just some niggling doubts alerted me to the possibility he may have connected it to the hot supply. The reasons are; The hot and cold pipes are arranged with the cold on the left and the hot on the right. When he connected the mixer he soon realised the glitch...he didn't really say why he did this. He fixed the problem by switching the flexible hoses around (easy). However, photographs I took when the pipes were installed show the copper "T" piece soldered to what looks like the hot pipe. I'm not saying he's wrong but I dont understand how it could be the cold pipe. Does this matter? If it is wrong can it be easily corrected?How can I know for sure?

dishwashers can be fitted to either the hot or cold water supply without and adverse problems ,the only difference is with cold water supply the internal heater will be on for longer to heat the water to the desired temperature as it will not be on for so long if connected to the hot water supply ,problems occur if your existing hot water system is small or a bit frail with age ,modern dishwashers dont use a lot of water so no real problem

Thanks Tom, I still want to know how I can check if its the hot pipe. Also, if its on the rinse cycle is it not more economical to use the cold supply?

the rinse cycle is only a flush with water and does not use a great deal so power wise its only using the water already heated in your system and to check which pipe it is just run the dishwasher through a cycle then feel the water connection the dishwasher is connected to and you will have your answer

My parents have the theory that if they connect their dishwasher to the hot tap then it saves power and time because it doesn't have to heat the already hot incoming water. This of course ignores the fact that their hot water cylinder now has to heat the replacement cold water..... Which one actually uses less energy is hard to say.

On the other hand, my dishwasher specifically says to connect it to the cold and NOT the hot tap, for three reasons: (1) the dishwasher can heat the water to the temperature *it* needs and not be dictated to by the temperature of incoming hot water; (2) domestic hot water is hotter than the dishwasher's 'light' cycle so in fact you'd be using more energy because the cylinder would be heating water hotter than it is required; (3) delicate crystal and things shouldn't be washed in water that is too hot which the dishwasher can't guarantee when connected to the hot water.

Bottom line: connect the dishwasher to the cold tap and let it do what it is designed to do.

Cold water connection is often recommended by manufacturers because it can also give a better pre-rinse: protein based food such as egg can be 'baked' onto dishes by a hot pre-rinse. A cold pre-rinse will rinse it off before a hot main wash starts.

Thanks for your responses all.....I see the sense in what you have said. The manual says to connect to the cold and this is what I prefer. It also says the water temp should not be above 55deg.C.
Now how do I fix the problem?

thats contradictory ,first off ,cold water is to state the obvious "cold" ,and the temperature of the water is dependant on the dishwashers heater . i think you are putting too much weight on this and either hot or cold will give the same results

Plumber insisted on wednesday it was hooked to the cold tap but I checked it this morning...it's definitely connected to the hot supply (the tap with the blue symbol ). Plumber made a mistake and will probably charge me to fix it

"thats contradictory ,first off ,cold water is to state the obvious "cold" ,and the temperature of the water is dependant on the dishwashers heater . i think you are putting too much weight on this and either hot or cold will give the same results"
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Tom Armstrong


Manual says cold is preferred...if you use the hot then it should not be too hot.
What I'm saying is I want what is the best method...I wanted the cold connection...plumber didn't ask me what I wanted...if he'd done correctly what he'd said he'd done, then I would be happy. He said it's the cold and it clearly isn't!

to regulate the heat you will need to fit a tempering valve ,these are not cheap,as you didnt give him clear instruction about which supply to fix to you havnt got much of a leg to stand on .i would ask him to check for himself on which pipe he has connected the dishwasher to and perhaps if he realises his mistake will change it for you gratis but i wouldnt be holding my breath if i were you

3 legs to stand on actually..., you must be his friend...He well knew what I wanted and he well knew what is correct and what isnt. I don't think a tempering valve is the answer..he should have used the cold supply...it was his mistake, he should fix it.So, I havent paid the bill yet...another tradie tries to deceive me, (gratis, ha ha)

i've been thinking about this post all weekend and after re reading your origional post came to the conclusion that 1. your pipes are installed the wrong way 2. whoever has placed the pipes this way has welded the connection for the dishwasher onto the hot water pipe 3.the plumber you have contracted to fit the connection has seen the existing t junction and has conected to this .
So really the plumber has only extended the services that you have supplied to him .
because you havnt been specific and told him that the connection was on the wrong pipe what was he to do ,run the water to find out if what you have supplied was correct ,no he connected to your fittings in good faith . its like asking a carpenter to come around and fit a door ,you already have the opening but you want the carpenter to feel around the wall and say that your door is in the wrong place and should be somewhere else
you neglected to mention that you hadnt paid the plumber so you already have leverage over him so why come here to ask ,why not just ring the plumber to tell him YOUR problem and let his professionalism handle the rest .
i think you should be finding and contacting the origional plumber that did the work to come back and correct his mistake ,but no that wont happen he's been paid !

For clarification. He's the original plumber whom nearly 3 months ago I have paid and who initially installed and soldered the pipes the wrong way...hot where cold is and vice versa...he soldered the dishwasher tap T junction to the hot pipe (he installed the hot pipe back to front) whilst I was at work.
He hasn't shown much professionalism....i.e; coming to my house to install the sink taps without the correct pipe connectors etc. to connect to the pipes he had initially installed, then sending me to the hardware store to find them; then charging me for 45 mins time he spent at tradelink getting flexible hoses for the gas pipe that he forgot to bring to the job with him to connect to the gas pipe he had installed previously

Hmmn. me thinks his mind was on another job...he was in too much of a hurry to get to another job he booked without finishing the job he'd agreed to do that day ie, installing a new HWS. I took time away from work to be at home that day, now I have to take more time off. He has to come back anyway, he said to pay him when the work was finished.

well then thats good "alls well that ends well"

The plumber put the 'tee' fitting on the cold tap and now the dishie runs off the cold...I'm happy about that...it may sound picky but ever since that fitting was placed the water pressure has dropped quite significantly...I guess it's not that much of a problem...just takes a longer time to fill the sink...any ideas why the pressure dropped?

is there a isolator tap underneath. If so it may not be opened fully.

Hi Borg, there is an isolator tap fully opened and makes no difference to the flow speed or volume

pulling at straws here but can it be blocked??
Perhaps there is a blockage at the tap end.
Water saving taps block easily.

Borg is probably right. Take the aerator off the end of the spout and clean it out. You probably got some muck through the lines when the plumber did his work and it has blocked the aerator/flow restrictor.