Low water pressure and washing machines

Low-water-pressure Low water pressure has become a big problem for a minority of washing machine owners due to the way modern washing machines work. Some people find that even though their old washing machine may have been slowed down by a lack of good water pressure, it was still able to complete a wash cycle.

Yet when they buy a new one it sometimes refuses to work.

Why is water pressure so critical now?

Stop-watch In the past, washing machines were controlled by simple mechanical program timers. When filling with water the timer motor in the programmer was turned off. The whole program came to a stop until the pressure system detected the right level of water had been reached.


It then powered up the timer motor, and the washing machine commenced washing or rinsing. This system was highly tolerant of low water pressure. It wasn’t dependent on time. It was just dependent on getting the correct amount of water inside eventually.

Washing machines are now far more sophisticated and most are controlled by software built into PCBs. The wash cycle is controlled like a computer program. This is an excellent advancement and brings lots of safety features and efficiency improvements.

One side-effect is that without a high enough water pressure many washing machines will detect a fault and abort the program – even if the same water pressure has sufficed for many years with the old washing machine.


Time-out The amount of time allowed to fill can vary from machine to machine. So some washing machines are more tolerant than others (more on this later). Some washing machines may allow too little time to fill and can abort the program unnecessarily at times.

The fact that the previous washing machine worked perfectly OK with the old mechanical timers backs this up.

How does low water pressure affect a washing machine?

When reaching a fill section, the programmer now no longer shuts off. Instead, the clock is ticking.

The software constantly checks to see if the correct water level has been reached. If the correct water level has not been reached before a pre determined time limit then the program times out. This usually triggers an error code, and aborts the wash cycle. When setting the time limit though, some manufacturers may set it slightly too cautiously.


Why do they do this?

Setting a predetermined time limit for specific events is a good method of averting potential disasters. It can prevent things like flooding or overheating. Suppose there’s a big hole in something and the washing machine is trying to fill the drum – but the water is just pouring onto the floor.

If unattended this could be a disaster. So if the washing machine times out after 3 or 4 minutes because the water level hasn’t risen inside the drum, this is very desirable.

Also, if water pressure falls below a certain level there is another safety issue because the washing machine fill valves need a minimum water pressure in order to close off properly. This can cause water to seep slowly into the drum and is arguably a very silly design.

What can you do if you have low water pressure?

There may not be an easy answer. Especially if you don’t have access to a mains water supply and rely on a bore hole or a well to supply water. In these cases you would need to do some research into using an appropriate booster pump.


It must be a pressure activated type i.e. pressurises the house water system to approximately 2 – 5 Bar (depending on pump used) even when off. You cannot use the flow operated type (as used for shower pumps).

Miele washing machines

If your washing machine is a Miele, it may be possible for one of their engineers to adjust the time limit on your machine to allow a little longer to fill.

I don’t know any other manufacturers that can do this, and I especially doubt most ordinary ones do but you could always try asking. If nothing can be done and you can’t fix the problem you may need to replace the washer with one more tolerant to low water pressure.


Miele’s technical manager has told me that their machines will work down to almost half a bar. So anyone affected must have a very low water supply. Also, Miele washing machines can be adjusted by a Miele engineer to adapt more to low water pressure situations. I’m not sure exactly what they do but I suspect they can increase the amount of time allowed for filling.

It’s a sign of the extra sophistication you get with Miele product but of course this is likely to be a chargeable service as it’s not addressing a fault on the machine. It should rescue you if you just laid out for a new Miele, which didn’t work due to low water pressure and the water pressure was only just too low.

The vast majority of people have perfectly adequate water pressure. This article is for those who are aware that they have very low water pressure, or for those where their water supply may be from an unconventional source such as a bore hole or well. In such cases some sort of pump booster would be needed if pressure was too low to run a modern washing machine.


What is 1 bar of water pressure?

1 bar is a pressure that’s capable of supplying water 10 metres high. So if water was fed to a pipe at ground level that was 10 metres tall there should be enough water pressure for the water to come out at the top of it.

Water companies in the UK are obliged to supply mains water at a minimum pressure of 1 Bar. Washing machines should be designed to work on a minimum of 1 bar so unless you have an unconventional supply you shouldn’t (in theory) be affected. I’ve been told by an Electrolux that their washing machines will work with a minimum of .5 a bar. Miele washing machines need at least 1 bar.

If concerned about very low water pressure, ask your local water authority what the water pressure is to your home. If they say it is 1 bar or over then modern washing machines should work. If not you would need to complain to the water authority that your supply isn’t good enough to use a washing machine with.

Of course you need to make sure nothing within the house is restricting the water flow like the stop tap being turned down low.


5 things to try if you have low water pressure

1 Make sure the tap supplying the washer is turned on fully. Also make sure that no fill hoses are kinked. Ensure the tap isn’t faulty. The ubiquitous taps with the blue and red levers in particular can often partially seize up inside. They can become caked in sludge inside, or the plastic operating lever can crack meaning that the tap appears to be fully on but it isn’t.

2 If it’s just general low water pressure all over the house and you have already got the main stop cock on full, get in touch with your water company who may be able to help. Water companies in the UK are obliged to supply mains water at a minimum pressure of 1 Bar. This should be high enough for a washing machine. If you don’t think your water pressure is particularly low, test by disconnecting the fill hose(s) and running the water into a bucket to check the flow rate in case the low pressure is just at the washing machine’s tap.

3 Don’t use those self-tapping self-plumbing taps that just clamp on to the copper pipe and pierce a hole to “tap” into the plumbing. Most of them pierce such a small hole (and often not cleanly either) that you probably won’t get a full water flow. In border-line cases it may be enough to prevent the washing machine getting the right amount of water in time. If you have those taps fitted and especially if you didn’t have trouble in the past then getting them replaced with proper taps may make a big difference.


4 If the washing machine is supplied with water by a header tank instead of mains water then it needs to be high enough to create an adequate water flow. However, raising it may not make enough difference unless you can raise it high enough and that’s not always possible. Here’s what Electrolux’s technical spokesman told me –

.. in order to obtain the minimum pressure, there should be a minimum vertical distance of 16.5 feet from the bottom of the tank to the top of washing machine. If this is not possible i.e. a bungalow or flat, then the only other option would be to fit a pump. However, this must be a pressure activated type i.e. pressurises the house water system to approximately 2 -5 Bar (depending on pump used) even when off. You can’ use the flow operated type (as used for shower pumps)

5It’s possible that your water pressure may vary, and be slightly stronger or weaker at certain times of day, especially if you live in flats. At weekends or after work for example it could be that more people are drawing on the water. So try changing when you put the washing machine on. It’s a long shot, but if borderline it could make a difference.

UPDATE: I’ve managed to get a comment from a technical person at Electrolux who make Electrolux, AEG, Zanussi and Tricity washing machines which may be of use to anyone with known low water pressure such as water supplied from wells or tanks. Here’s what they said ..


All of our washing machines are now electronic and incorporate a maximum time fill of 10 minutes, the minimum water pressure required is 0.5 Bar (Maximum 8 Bar), this minimum pressure is required to ensure that the valve closes completely, (if less than 0.5 Bar there is a possibility of water entering the machine even when off electrically).

In low water pressure areas, we recommend that the machine is tank fed, but in order to obtain the minimum pressure, there should be a minimum vertical distance of 16.5 feet from the bottom of the tank to the top of washing machine. If this is not possible i.e. a bungalow or flat, then the only other option would be to fit a pump. But this must be a pressure activated type i.e. pressurises the house water system to approximately 2 -5 Bar (depending on pump used) even when off. You cannot use the flow operated type (as used for shower pumps)


Anyone looking for a pump to increase their mains water pressure should Search Google for – pump increase water pressure

Further update:

A comment from Tim (below), has highlighted a Panasonic washing machine, which he says works as low as 0.3 bars and has got it working in his low water pressure situation.

Update:

A design anomaly or flaw with washing machine water valves is that very low water pressure can cause the washing machine water valve to not shut off properly allowing water to seep into it overnight. This shows the reason why manufacturers say you need a certain minimum water pressure although in this particular case it was caused by a faulty tap that didn’t actually shut all of the water off reducing the water pressure down so low the valve couldn’t shut of.

It does seem a very flawed method of stopping water from entering a washing machine, that is, using the pressure of the water itself to shut off the valve – when if the pressure falls below a certain level it fails to shut it off.

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102 thoughts on “Low water pressure and washing machines”

  1. Why the rinse cycles are not affected by low pressure ?

    The time out only applies at the beginning of the wash cycle. So a simple press of the play button resets it. There is no time out for the rinse cycles.

    It seems odd to enforce the time out at the beginning and not for other water filling cycles as well but this is what can be deduced empirically.

  2. The rinse cycles should still be affected by the time out. If it hasn’t reached set levels before a certain time the machine decides there must be a filling fault. It may be the time limit is slightly more generous for rinses for some reason.

  3. Gorenje manual, states the following..

    “To ensure correct operation of the appliance, water pressure inlet must be between 0,05 and 0,8 MPa. Minimum water pressure can be established by measuring the quantity of poured out water. 3 litres of water must be poured out from completely opened tap in 15 seconds.”

    Gorenje wants a minimum flow rate of 12 litres per minute compared to 8 litres for bosch/siemens.

    Even though the minimum incoming water pressure is 0.5 bar, the flow rate or what the machine expects also matters.

  4. Another possibility is that a lot of the initial water gets soaked up by the dry laundry when it first fills. Also, it’s more critical on wash because if there isn’t enough water in the heater may not be covered, which would be very bad.

  5. More low pressure revelations, this time from Panasonic (generic model#s NA-107VC4 & NA-127VB3)

    “Optimum mains water pressure is 0.1 – 1.0 MPa. If the water pressure exceeds this value, install a pressure reducing valve.

    Water-flow from the tap should be more than 5 L/min.”

    which corresponds to 1-10 bar pressure. However the 5 litres per minute requirement is odd. A 1 bar minimum pressure means roughly at least 10 litres per minute. Yet the Panasonic manual states it can handle half that amount. So the timer is not going to trip if the water pressure slows down to that rate so long as the flow stays above. But what about the inlet valves. If they’re spec’d for 1 bar minimum then a low pressure most of the time may not work out too well.

    What isn’t clear is whether it wants a 1 bar minimum pressure most of the time and can handle pressure as low that amounts to 5 litres/min or

    Whether it will function at all if the flow rate is little over 5 litres per minute but less than 1 bar. A crucial distinction.

    It makes me wonder which is the more important parameter to take into consideration. The incoming water pressure or the flow rate ?

  6. No, flow rate and pressure are not equivalent in the sense there is no way to derive one from the other. Flow rates are provided i would assume so that there is some easy way to measure whether enough water arrives to satisfy the timer.

    My tank is at a height of little over 6 metres (20 feet) and i get a flow rate of around 6.5 litres/min. Rough correlation there between height in metres to flow rate.

    The variance in flow rates stated in the panasonic & gorenje manuals is noticeable, former says 5 latter says 12 L/min with bosch/siemens falling in the middle with 8 L/min. All 3 spec a minimum incoming pressure of 1 bar.

    So Panasonic’s timer is little more forgiving than the germans and so on compared to Gorenje.

    But you said in the article that incoming water pressure is required to close the inlet valve. I’ve not understood how, if the timer were reset one time to allow more water to fill that the valve closes eventually at all if the pressure stays low. If the valve does indeed close eventually then its the machine that closes the valve at some point irrespective of the water pressure.

    Update

    my mistake gorenje stated 0.5 bar to 8 bar. still the flow rate of 12L/min does not correspond to 0.5 bar in my opinion. The gorenje timer will time out and give errors.

  7. To me they are the same. It’s like comparing how much energy someone puts into a run using the scientific measuring system of joules with how far he actually runs. So you might say an athlete uses 1000 joules or the 1000 joules enable him to run 500 metres. If you know an athlete can run 500 metres on 1000 joules you could use the distance as a crude way of describing using 1000 joules. (That’s a very crude analogy but hopefully it works :) )

    Unless I’m totally misunderstanding something that’s what the flow rate is being advised for. The manufacturers know most people can’t measure water pressure so they say if water pressure is 1 bar it should fill up x amount of litre jugs?

    My article quotes a source which says, “1 bar is a pressure that’s capable of supplying water 10 metres high. So if water was fed to a pipe at ground level that was 10 metres tall there should be enough water pressure for the water to come out at the top of it.” This is just another variation on the filling 3 litres of water in 15 seconds test for between 0.5 and 0.8 MPa

    I would expect that the flow rate is defined exactly by the water pressure. :)

    The old system by the way, when they just waited until the right amount of water went into the machine. Even if it took 10 minutes it would still work. I used to go to washing machines which took an extra 15 minutes to complete a wash cycle but still worked perfectly OK. The only reason they should be worried about very low water pressure though is if it’s so low the valve doesn’t shut off properly and water seeps in. This did used to happen, but rarely. I can only assume they introduced these time limits of fill to detect water pressure being so low the valve won’t shut off.

  8. Spoke to a couple of people who had the following models

    Siemens WM07A160ME with the overhead tank 20 feet above.

    Bosch WAG14060IN with tank just 9 feet above.

    Manuals for both state minimum 1 bar pressure. The owners have had no problems in operation with either at all. The Bosch was a real surprise, you’d never expect it to work but it does. I asked them to measure flow rates but they were not forthcoming. There is no way either gets anywhere close to 1 bar pressure.

    The common point with both these two machines is they have no display. So no way for the machine to display any 2 letter error codes.

    Just because it worked for those models does not mean it will work with others. I notice those two models have been discontinued and even the basic models for either brand these days have displays.

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