Low water pressure has become a big problem for a minority of washing machine owners because of the way modern washing machines work. Some people find that even though their old washer 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 replacement it sometimes refuses to work.
Why is water pressure so critical now?
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 because 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 which runs like a computer program. This is an excellent advancement and brings lots of safety features and efficiency improvements but 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.
The amount of time allowed 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 abort the program unnecessarily at times. The fact that the previous washing machine worked perfectly OK with the old mechanical timers tends to back this thought 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 and the software constantly checks to see if the correct water level has been reached. There is a pre-programmed time limit, and if the correct water level has not been reached before this time then the program times out, triggers an error, and aborts the programme.
Why do they do this?
Setting a predetermined time limit for specific events is a good method of averting potential disasters and preventing things like flooding or overheating. There is a genuine safety issue if water pressure falls below a certain level because the washing machine fill valves need a minimum water pressure in order to close off properly. When setting the time limit though, some manufacturers may set it too cautiously.
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 well to supply water. In these cases you would need to research using an adequate booster pump, but 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)
Here are some things you can try -
Make sure the tap supplying the washer is turned on fully, and that no fill hoses are kinked. Also make sure the tap isn’t faulty. The ubiquitous taps with the blue and red levers in particular can often partially seize up inside, 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.
If the low water pressure is only to the washing machine and you’ve done the first checks get the plumbing checked. 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, which should be high enough for a washing machine.
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 washing machine is supplied with water by a header tank instead of mains then it needs to be high enough. However, raising it may not make enough difference unless you can raise it enough. 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, 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)”
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 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 (mentioned below).
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. However, 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.
Please note / Summary
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 (Water companies’ contact details). 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.
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 -
“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 try this Google search Search Google for pump increase water pressure
Further update: Oct 2010
A comment from Tim 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 Comment 51
Update: May 2011
A comment from Faith highlights the problem of very low water pressure causing the washing machine water valve not to 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.