Can you connect a dishwasher to the hot water supply?

This article was inspired when comments from another article ventured into the subject of whether you can connect a dishwasher to the hot water supply instead of the cold. This doesn’t appear to have a clear-cut yes or no answer.

There is conflicting advice, even from dishwasher manufacturers. Some claim it’s more economical but others say it’s better to run a dishwasher using cold water.

Most dishwashers in the UK are supplied with a cold fill hose and with instructions to connect it up to the cold water supply. Most people do connect it to a cold water supply and they work perfectly well. Many dishwashers are designed to work by heating up water from cold.

Some dishwashers can be connected to a hot water supply though. If so, it should say so in the instruction manual. If you do connect a dishwasher to the hot supply you should use a hot fill hose, which is designed for use with hot water. I’m not able to emphatically say that connecting a cold water hose to a hot water supply is running any risk.

But fill hoses have always come as either hot or cold. Either in red or blue, or with a red stripe or blue stripe. So the implication is that they are different in some way. If this is pure marketing spin I wouldn’t be too surprised. But it is reasonable to expect that the individual requirements for hot and cold water are different enough to require specialised hoses.

Pros and cons of connecting a dishwasher to hot water

The next sections look at some of the advantages and disadvantages of using a dishwasher connected to a hot water supply.

Pros –

Depending on how your hot water is generated, it potentially saves electricity. Dishwashers often wash at high temperatures. They also often use high temperatures for the last rinse to aid drying. However, If using hot water is so much more efficient, why aren’t all dishwashers coming with recommendations to use hot water? Why don’t manufacturers advise that cold water can be used if preferred – instead of the other way round? The answer may be very much related to the same question about cold fill only washing machines

Quicker wash times

If you can get hot water into the dishwasher efficiently, that is, it doesn’t take a long time to start running hot. Then wash times can be speeded up.

Cons –

If the water entering the dishwasher is over 60 degrees it can damage the filtration system built into dishwashers. So don’t use hot water if this is the case. My understanding is that hot water should only be set to 60 degrees anyway, which is the optimum setting for a hot water supply in most homes. But some people may have set it higher.

Hot water supplies may not have the same water pressure as cold, especially if supplied through a hot water cylinder in the airing cupboard. Hot water hoses are more prone to kinking too, so you would need to ensure the hose isn’t under any physical strain at the back because when hot water runs through it, the hose can go soft and develop a kink.

If the initial water is hot it can bake some food onto plates and make it more difficult to clean.

Dishwashers often have a 50 degree wash cycle. If the water inlet temperature is already 60 degrees this programme may be compromised.

If you want to check your dishwasher can use hot water but don’t have the instruction book you may be able to download one here – download instruction manual for washing machine or other white goods appliance

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49 thoughts on “Can you connect a dishwasher to the hot water supply?”

  1. I suspect dishwashers would add some cold to the main wash to cool it down before draining it out and rinsing. Maybe even pump some out, add cold, pump a bit more out and add a bit more to slowly reduce the temperature safely. Any dishwasher that cracked anything simply because it rinsed in cold water right after heating up the crockery wouldn’t be ft for its purpose and could be returned under the Sale of Goods Act.

  2. If you’ve ever looked in the bottom of the header tank that feeds the hot water supply you wouldn’t use it in a dishwasher.Years of sediment plus what can get in if it’s not covered properly,I’ve seen dead bats,mice and rats in them over the years.
    Direct feed from a heater is safe enough but hot water from a storage tank is to be avoided.

  3. The reason why all hot water systems heat to 60C (higher in the case of some solar and solid fuel systems) is that 55C is generally accepted to be the killing temperature for Legionella bacteria in hot water systems. So for a tanked system, if the hot water in the tank reaches 60C at least once every 24hours and each hot outlet (tap) is run every 24hours there should be no legionella. I mention this because it would be very bad if your readers turn down their hot water thermostats to save gas/electricity. Legionella is ubiquitous in the environment so their system will become infected.
    In contrast hot water is dangerous at above 42C. But you need 50C at the kitchen tap to clean greasy dishes So their is a safety trade off. Hence thermostatic mixer valves at bath taps/showers or washing facilities where children/elderly/disabled wash (healthy adults have good enough reactions to stop themselves getting scalded. Check out the CIPHE for details on this issue.
    I have plumbed my dishwashers into hot supplies in my own houses and have noticed no detrimental effects on the dishwasher/dishes or hoses over many years. One solid fuel system I had used to generate HW at much hotter than 60C (I had problems with it boiling) and yet the standard cold fill hoses still seemed to survive OK.
    When I plumb dishwasher in for my customers who have non electric based HW systems I always tell them this and give them the option of HW fill. For gas/solid fuel/solar systems this affords a considerable saving over the life time of the appliance as electric heating at the appliance is more expensive per unit of heat. Non of my customers have noticed or complained of any detrimental effect caused by HW fill, over many years. This includes some commercial kitchens where the dishwasher hardly ever stops. The only disadvantage is that if you have a combi boiler or water heater it will keep firing up every time you turn on your dishwasher, but that’s the sound of you saving money!
    I have not noticed any problems caused by low pressure HW supply to the dishwasher.
    In practise I think all dishwashers/washing machines etc should be duel fill. Further efficiencies could be produced by linking the devise to the HW cistern or boiler so that the devise “chooses” to use HW when it is available thereby using HW from the cheapest most environmentally friendly source.
    Nick the Plumber

  4. I’m keeping my dishwasher connected to the hot water supply. It has never smelled inside since using the hot supply. No negative points at all. Yes, you will need to run the nearest hot tap before switching on the dishwasher to make sure it fills with the hot water – this takes about 1 minute and saves £££’s on the electric bill (provided the hot water is heated by anything other than electricity).

    I still give the dishwasher monthly cleans with Affresh dishwasher cleaner, using Affresh in the empty dishwasher on the hottest programme. A combination of a hot supply and monthly cleans with Affresh dishwasher cleaner must be keeping the internals spotless and avoiding expensive breakdowns from fat and food blockages. Yes I keep the filters clean, but they don’t seem to get so dirty since having the hot water connection.

  5. You will find all modern machines will be cold fill only. There is a very good reason for this and it has to do with overall energy use and efficiency in regards to the hot water.

    Basically, most modern domestic hot water systems are extremely efficient and can reach high temperatures. The washing machine or dishwasher is normally using the water at a lower temparature than the domestic boiler is heating it to.

    For instance, if your hot water boiler gets the water to 85 degrees, and the washing machine only needs to use it at 60 degrees, then you will be wasting energy. Your boiler has spent energy to heat the water up to 85 degrees, and then the washing machine is adding cold water to it to cool it down to 60 degrees.

    Therefore the new method is for each machine to heat its own water measured to the precise use. It is more economical for the machine to heat a small amount of water to the exact operating temparature, than for that temparature to be reached by your hot water boiler and then cooled down.

    There is no technical reason why you cannot attach a machine to a hot water pipe. The machine will use its internal thermometres to reach the correct temperature. Just be aware, that you may be burning money by heating water up in your boiler and then cooling it down in the machine.

    That is the basic rationale behind all dish and clothes washing machines being cold fill only.

  6. Reading the comments, it is of course dependant on situation.

    I would say if you have a new style modern combi boiler, and a newish machine, you should stick with cold fill, because that is how they are designed, and the efficiencies will work towards you.

    I have a friend who runs a solid fuel water heater and a hot water tank. The water is heated only when there is a fire of course, so it is not on demand when you turn on a hot tap like a it is with a combi, so he can end up with a tank of warm water that is slowly cooling down and not being used. Therefore in his situation it is more economical to use the hot water on the cold fill, because that water has already been heated once (your combi boiler heats the water when the machine asks for it). Otherwise his machine would be heating cold water while there is hot water standing around getting cold.

    The key is in how you heat your domestic water.

    If you have hot water on demand, usually a combi boiler – use cold fill
    If you heat your water some other means and store it, then using the hot water on the cold fill may be more economical.

    I worked in customer services and around 10 years ago this was a massive issue for customers. People were very very angry that their new washing machines only had a cold inlet, a large number of people demanded that we replace the machines with dual fill – which was not possible. Every manufacturer took this up across a very narrow span. It took a lot of effort to get the message across to the consumer.

    One day there may be a smart device to communicate between the machines and your combi boiler will deliver the exact amount of water at a precise temparature as demanded by your washer, and we’ll be back to hot and cold fill machines again!

  7. There’s progress in the world!! Purchased basic Bosch Dishwasher. Can be fitted to hot water supply only. This is good for me because:

    No Mains gas
    Solar hot water
    Less than 2 litres draw off from hot water tank to dishwasher.
    Thermostatic water blender set to 55 deg C.

    Will test this during the summer and advise..

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