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. Chris Ogilvie

    Our house is fed by a spring which gives pressure of 0.2 bar at the kitchen tap. It’s excellent water and never fails, and we’re too far from the mains to receive mains water. Our 15 year old AEG washing machine, now sadly defunct, coped with the low pressure by having an internal reservoir which filled at its leisure. Thanks for the info about modern washing machines, all of which seem to require a minimum pressure of 0.5 bar. The remedy recommended by Zanussi as above is to pressurise the entire system rather than use a flow activated pump specifically for the machine. We don’t want to do this as it might find joins in the plumbing that are tight for 0.2 bar, but no more. Why is an individual flow activated pump not suitable?

  2. Hi Chris: I agree, if you pressurised the whole system you have a chance there could be leaks. I don’t know of any reason why you can’t use a suitable pump designed to boost water pressure to a specific point.

    There is no difference between the way your old washer worked and the new one apart from the old one waited until there was enough water in before starting to wash, but the new one times it and panics if it hasn’t filled to a certain level by a set time. New washing machines are run by software like a computer program built into the main pcb. This set time is strict and doesn’t allow for very low water pressure.

    Most manufacturers would say 0.2 bars is so weak it can’t shut the water valve properly and you could get seepage of water into the washing machine when not in use if the taps are left on. This is why they impose a strict time limit. If a washing machine hasn’t filled by their set time then the water pressure must be too low and in their opinion not safe to operate.

  3. Hi, Andy: Thank you for your helpful comments. We decided to go for a normal modest range washing machine, leaving ourselves with the following options: 1) hope it works! 2) fit individual booster pump as you suggested 3) build special storage reservoir higher up hill and pump water up when required. Luckily, we seem to have got away with option 1, although, as I said before, our water pressure is nowhere near the recommended minimum of 0.5 bar. The machine we bought is an Indesit WIXL 163 and seems to be coping very well, although so far we have been careful not to use other facilities eg showers, toilets, etc; at the same time as the washing programme is running. We spent a couple of nights in a B & B last month where they had a similar problem and were successfully using a 5 year old Hotpoint machine, currently out of production. Will let you know if any problems crop up. Chris.

  4. Robert Gilligan

    Our Hotpoint Top loader of 16 years faithful service as now stopped due to a water seal that is no longer available. We live in a remote farmhouse bordering the Yorkshire Moors with a spring water supply which is fed via a pump to the Header Tank in the roof space. The tank supplies both the cold taps and hot water cylinder, therefore the pressures are equal. The height from the washing machine inlet to bottom of the header tank in the roof space is 4 metres .We measured the water flow rate from the tap adjacent the washing machine, using an empty 4 pint bottle of milk, It took 15 seconds to fill this to overflowing.
    We found that new washing machines do not like low water pressure and have created problems that were not there before. Fortunately your articles have endorsed this so we did a little research and discovered:-
    Most new washing machines have cold supply only and the owners manuals gives the following water pressures as permissible operating minimum pressure:-
    Indesit, Zanussi, Hotpoint, Samsung and AEG = 0.5 Bar pressure.
    Bosch, Mele, Whirlpool and (LG Steam only) = 1 Bar minimum pressure.
    Some LG and Haier = 0.3 Bar pressure.
    But,
    The LG. Conventional Washing machines i.e. WM16336 and WM14336 are still available with hot and cold supply and only require 0.3 Bar minimum pressure. This applies to some of there cold supply machines also.
    So we now have a LG WM 16336 from CURRIES with a hot and cold feed and it works fine, thankfully we did not have to fit a water pump, and also our hot water cylinder supplies the machine, so we do not have to wait for it to heat up, it starts washing immediately
    I put some figures together in the table below to simplify things, for example in my case we have 4metres head of water which = 0.4 Bar which =40kPa which = 0.04Mpa
    The LG machine only required 0.3 Bar so we were well within the limits.
    Machine manufactures seem to use these units of pressure i.e. Bar, kPa and MPa . So you can see the relationship that 1Bar = 10 metres head of water therefore 0.1Bar = 1metre Head of water .Look at the manufactures Handbook in the shop or ask the sales assistant and you will find the minimum pressure required for that machine

    WATER PRESSURE (Approximate Equivalents)
    Bar Pressure Metres head of water Feet Head of water PSI pressure kPa pressurer MPa pressure
    0.3 3 9.84 4.27 30 0.03
    0.4 4 13.12 5.68 40 0.04
    0.5 5 16.41 7.11 50 0.05
    1 10 32.81 14.22 100 0.1
    2 20 65.62 28.44 200 0.2

    [Edit by Washerhelp]

    These figures kindly provided by Robert.

    The left column shows Bar pressure and the second and third columns show the equivalent height water should be forced through a pipe (although pipes with different bores may produce different results – I’m presuming a garden hose pipe would be accurate enough)

    Example:

    If you check 1 bar in the left column you can see this pressure should cause water to be pumped to a height of 10 metres or 32.81 feet.

  5. Very interesting article thanks.

    With regard to measuring water pressure, there is a useful statement in our Bosch machine’s manual (which frequently times out on fills presumably due to not being on mains but fed at too low pressure from a low header tank in our flat) which says that the 1bar minimum pressure required should produce a flow rate of 8 litres per minute. Sure enough we disconnected the input hose, pointed it into a bucket and found we were only getting 5 litres/minute.

    We’ll be looking to replacing it with one of the makes you mention supports 0.5 bar.

  6. All John Lewis own brand laundrey cooling dishwashing
    and finally built in products have a 3 year parts and labour guarentee.
    Top end JLP OWN BRAND WASHING MACHINES HAVE A FLOW METER
    Also AEG 7 AND 8 SERIES washing machines.
    Finally ZANUSSI JETSYSTEM PLUS washing machines

  7. 5 years ago I replaced my washing machine (H+C fill) for a Miele washing machine (Cold fill) and returned it within a week, due to low pressure error. As this was the first time I experience this type of problem I did a little research and came to the same conclusion as yourself, regarding H+C verses Cold only fill machines, and Mechanical verses Software driven systems.
    I have a standard 4 bedroom House with a Tank fed Hot + Cold water system which is approx. 5m high, which by my calculations gives me about 0.5 bar -the Miele Washing machine required 1 Bar minimum, hence my problem at the time.

    Luckily, 5 years ago there were still some H+C Machines available. I bought a Hotpoint WF860 with Electronic controller and H+C fill, which incredibly only needed a minimum of 3 psi or 0.2 bar!! and never had any issues with low pressure errors. Due to heavy use I am looking at replacing my washer, but finding it almost impossible to find any H+C machines now. As mentioned by Robert (comment #34) some makes will still run at 0.5 bar.

    I am looking at a Hotpoint AQ9D69 which is cold fill with Electronic Control which should run at 0.5 bar. Hotpoints reply to my enquiry about Tank fed systems was “Generally our appliances are set up to operate on mains pressure between 0.5bar – 10bar, however water from a tank presumably gravity fed may cause a problem if it falls below the minimum valve operating parameter.
    Unfortunately its not set in stone and you need to be made aware the appliance may not operate correctly.”

    I have talked to my neighbours (similar House and water system) to enquire what machines they are using and the minimum pressure specified -theirs work OK with a spec. of 0.5bar. Those with a similar situation might also consider talking to their neighbours -most people like to be helpful.

    Finally if an old Solenoid closes at 0.2 bar why do they specify 1 bar to keep it closed?, and if the machine is left powered on but in standby, why can’t the water level be monitored and automatically pumped out if it rises, giving a warning that a fault occured, without flooding the kitchen. -one for the manufacturers

  8. Thanks for your contribution Andy:

    Finally if an old Solenoid closes at 0.2 bar why do they specify 1 bar to keep it closed?”

    They would need to build in a safety buffer. If they allowed water pressure that was just strong enough to work ok then any drop in pressure caused by other appliances or taps drawing water at the same time or maybe even partial blockages or kinks in pipework etc would cause the valve not to close. By specifying at least twice the pressure actually required it allows for it to drop by half and still be safe.

    ..and if the machine is left powered on but in standby, why can’t the water level be monitored and automatically pumped out if it rises, giving a warning that a fault occurred, without flooding the kitchen?”

    I remember Hoover washing machines used to activate the water pump if the water level rose dangerously high even if the washing machine was not operating as long as it was left plugged in. Many people turn off their machines after use so any such method couldn’t be relied on but it would be a good idea for machines to detect water rising inside the machine even when not operating and operate the water pump and produce a warning.

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