Connect a cold fill washing machine to the hot water tap

Do's-and-Don'ts I’ve had several people ask if you can connect a cold fill washing machine to the hot water tap instead of the cold one. They were unhappy about the disappearance of the hot water valve in UK washing machines, and were wondering if they could circumvent the change.

Many people who are using solar powered energy to heat their water, or who had another cheaper environmentally friendly supply felt that the advantages of their environmentally friendly and economical hot water will be wasted by not using their hot water supply.

However, the answer to the question is no, for the following reasons..


Hot water supply is too hot

The incoming water temperature would be too hot (usually at least 60 degrees Centigrade). This can damage delicate laundry and shrink woollens.

There would be no way of controlling the temperature of the water going into the drum and onto the laundry.

A washing machine designed to use hot & cold water will control the temperature of the water in the drum by either filling with a mix of hot and cold – or filling only with cold water on all wash cycles except the really hot wash.

Too hot for most wash cycles

The temperature of household hot water is also too high for most commonly used wash cycles, which only need 30 or 40 degrees.

It is pointless putting on a wash cycle that needs to heat the water up to 30 or 40 degrees if the water is 60 degrees from the start.

So apart from potentially damaging some laundry, the washing machine’s thermostat would close almost immediately and the wash cycle would move on to the rinsing too soon. This would shorten, but compromise the wash quality.


Hot water not good for biological detergent

Biological detergent contains living enzymes. These enzymes are killed off at the temperature of most people’s hot water. So filling with hot water only would again compromise wash efficiency when using biological detergents.

Biological detergent is more effective when starting in cold water with the water gradually heating up.

Rinsing in hot water is very bad

If a washing machine is only connected to the hot water supply then obviously when it comes to rinsing the laundry – the water going in would also be hot.

So the laundry would be rinsed in hot water. This would cause severe creasing, as well as wasting all the hot water and being very energy expensive. Also hot water tends to activate detergent and create suds whereas cold water doesn’t and is therefore more likely to be better suited to rinsing laundry.

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What about connecting both hot and cold hoses to a cold fill washing machine?

Hot-water-plumbing You can’t swap the cold water supply for a hot supply for the reasons given in this article. However, there might be an argument for using a y-connector to connect both hot and water supply at the same time. However, this seems a lot of trouble for little benefit. You would need to manually adjust the water pressure of both supplies to get a balanced, “warm” combination.

But as hot water usually takes a while to run through the pipework, the chances are it wouldn’t use much if any on the wash cycle anyway. This is in fact one of the main arguments for cold fill only machines. It would do all the rinses in warm water, which may (or may not) be better. But it would also use a lot more energy.

A full explanation as to why almost every washing machine is cold fill these days is here – Pros and cons of hot and cold fill verses cold fill washing machines

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63 thoughts on “Connect a cold fill washing machine to the hot water tap”

  1. I don’t really believe that there are any disadvantages to having a machine that takes in hot water. I too had various machines over the years that had proper thermostats which meant that they took in hot water until the correct temperature was reached and then switched to cold. The programmes were quite sophisticated, with some taking in cold water initially where this was more appropriate. Most plumbing systems would give a short run of cold first (which I could run off for another purpose using an adjacent tap if I had time). I believe that the only disadvantages are those for the washing machine manufacturers who don’t have to put as many parts into a cold fill only machine. We run our machines at night on cheaper electricity and it makes sense to use up some of the hot water remaining in the tank.

  2. I have a cold fill washing machine but by using a thermostatic mixing valve set to deliver the hot water at the lowest wash temperature (30 degrees centigrade) this will not compromise the wash quality. As for the cold water draw off I have installed a secondary circulation circuit from the cylinder to shorten all the dead legs in the house as a whole. In the case of the bathroom, the taps required a minute to reach temperature, now only a few seconds are required. The washing machine only draws about half a litre before the hot water is delivered. Obviously this is a large undertaking for just the washing machine as the savings will not cover the cost of the upgrade, however, if you are contemplating upgrading your plumbing system anyway it is worth considering.

  3. we have a Hoover washing machine that requires the use of both hot and cold water supply. Is there a way of adapting the machine to only use cold water

  4. Re Martin’s comment: my daughter has a flat with a service charge which includes all hot water and heating so we are adding a cheap thermostatic valve to deliver water at 40 degrees. This will be reduced by the (short) dogleg of cold water and the heat lost in warming up the cold machine.

  5. after reading only part way through, the defeatist attitude of repliers decrying the need for hot fill was disheartening.
    simple solution for hot and cold fill wm’s:
    connect cold to wm/cold,
    connect cold to thermostatic mixer, connect hot to thermostatic mixer, connect thermostatic mixer to wm/hot, set mixer at 30-40. Initial hot intake will be cold from pipe till hot reaches mixer then water intake will be at preset temp of mixer.
    If your hot water system is a loop for instant hot at the tap, then spur off the loop with zig zag arrangement a few metres long, ours is under the kitchen unit kickboards, then into the mixer valve. This ensures the initial charge of water is not too hot for biological powders.
    All this is pointless unless your hotwater source is really close to the washer.

  6. The cold pipe to our kitchen developed a pinhole corrosion leak, as evidenced by water coming out of the floor. Great joy. Our eldest then arrived home with an enormous bag of washing. Faced with this combination, the obvious question is – can I connect my cold fill washer to the hot tap that dates from the time of its predecessor? As I am made from biological materials, I do not use powder with enzymes it in because I found that they eat my skin; this means that we do not have the problem of the enzymes not working. So the only problems that seem to apply is the danger of delicate fabrics being damaged (don’t think he has any of those!) and excessive creasing (don’t think he is that worried!). Faced with going through insurance and waiting months; getting a plumber and waiting weeks; or getting out a hammer and bolster (Why do they put concrete on top of water pipes? Definitely a decision made by the sort of people who choose chipboard as a material for under-sink cupboards); the temporary expedient is a choice between hot fill, do it in the bath or drive to a launderette.

  7. Andy Trigg (Whitegoodshelp)

    Hello Alan. Yes my article mentions all of the downsides, not least the extra cost of wasting hot water, damaging delicate laundry, and causing excessive creasing. If you’re aware of all the problems and want to try that’s up to you but it’s definitely a bad idea. However, I appreciate you might be desperate. If you could, just don’t put the hot water on, or wait until the hot water has been used up. Then you could use the washing machine with the hot water supply and as long as the water pressure was adequate the washing machine wouldn’t notice any difference. Pretty much all of the disadvantages would disappear if the hot water supply wasn’t actually hot.

  8. Main question is how much is this hot water already costed you before it will be used in washing machine?
    Then what would be the required temperature rise from cold tap water.
    I think that if the smart washing machine or dishwasher would be programmed to be able to recognize whenthe actual hot water would be good for certain cycle(main wash,prewash) that would be the way to go forward and couldn’t see it being a big problem to solve for big manufacturers. It could have a very eco selling pointbregardless how real are the saving on energy or how to measure saving for ordinary buyer at home. I’m always using the shower head and while the by me decided cycle is starting by just adding hot water via washing chemicals little drawer. Just open it and ad hot water it will be cooled down a bit by mixing up with water coming by program requirements but I normally check the temp on glass of the door and it is definitely warm. Did it from kettle before moved to a place with long enough shower pipe or hose or how does it cold.

  9. Andy Trigg (Whitegoodshelp)

    Hello rad. The biggest problem is that hot water coming into a washing machine is never instantaneous. Even with a combination boiler, if everything is set up okay, hot water can reach the washing machine reasonably quickly – but still potentially not quick enough for most settings. Any washing machine supplied with a hot water pipe that has quite a long pipe run from the boiler will take a while to deliver hot water because all of the previous hot water that had been drawn in has since has cooled down and gone cold.

    With hot water supplies in the UK commonly being delivered by a hot water cylinder in an airing cupboard upstairs, this problem is even worse. It can take so long for piping hot water inside the tank to actually get to the washing machine that with today’s washing machines hardly using any water the washing machine has just about finished filling up by the time any hot water arrives.

    The only way around this involves wasting water or trying to recycle it but with no room to store it . Temperature sensors on the incoming water could divert the water from the drum and from washing in the detergent until it gets to the correct usable temperature. But this water would need to be diverted to a separate container and there is definitely no room for one in a modern washing machine. Or alternatively it would have to be pumped away down the drain instead. So one potential problem is solved by causing water wastage.

    So it is technically possible for manufacturers to utilise hot water intelligently and effectively, but only at the expense of wasting water, or trying to recycle the unneeded cold water in the hot pipes later on by storing it in a container somewhere inside the washing machine. It is just completely impractical to do so. So it’s either go back to hot and cold fill washing machines (that for most people means hardly any hot water getting into the washing machine) or use cold fill only and heat up just the right amount of water that is needed for the wash which is the current trend. In the great scheme of things, looking at the most common scenarios and the most common requirements it is by far the most sensible way of doing it.

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