Faults on Pressure System

Failed I have a previous article describing exactly how a washing machine controls water levels. This article is a follow up to it describing some of the faults that can occur with the pressure system on a washing machine or Washer dryer.

What is the pressure system?

The pressure system is made up of several parts. It has a simple purpose and that is to tell the washing machine when water inside the drum has reached a specific level, and when all the water has been successfully pumped away. If something goes wrong and the washing machine does not receive these signals then the washing machine can either overfill, or refuse to spin.

Various things can go wrong causing symptoms described below – but all these symptoms have other possible causes too. So it’s important not to make assumptions. In order to try and understand pressure system faults you should read the first article to understand how the pressure system works.

Pressure-switch_2 They are normally very reliable, but it’s possible for a pressure switch to be faulty.

The pressure switch

However, in my experience it is the last thing to suspect. Never fit a new one if you haven’t ruled out all other faults – especially a blockage in the pressure chamber bottle at the base of the outer drum (details later). A switch sticking on will make the washer think there’s water inside the drum when there isn’t. Conversely, sticking in the off position will tell the washer there isn’t any water in when there is.

The former would cause the washing machine to not do the fast spin. The latter would cause it to overfill. However, neither of these symptoms are exclusively related to a stuck pressure switch – there are more likely causes. Remember, a pressure switch is far more likely to be stuck because of a blockage.

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The modern pressure switch

modern pressure switch The pressure switches shown and described above have now been replaced with a different type. Instead of having mechanical switches inside that are operated by air pressure they have small coils with magnets inside that give a different resistance reading depending on how much air pressure is applied.

The old style pressure switch has remained virtually unchanged for 40 years or more and has usually been one of the more reliable parts on a washing machine. It remains to be seen whether these (obviously cheaper) designs are reliable or not but in theory they ought to be very reliable still (if not more so) because of the reduced number of parts. Troubleshooting these modern pressure switches may be a bit more difficult without knowing the expected resistance readings.

The small pressure switch tubing between the pressure switch and pressure chamber bottle

Pressure-tubing Damage to the pipe, or air leaks at the connection points on the pressure switch or plastic pressure chamber bottle can cause overfilling because air pressure is lost. Without an airtight connection it’s impossible to create enough pressure to activate the pressure switch or at last to keep it switched on..

Pressure chamber bottle

If the pressure chamber at the bottom of the tube gets blocked with gunge inside, then when the washing machine empties the water, the water inside the pressure chamber (which is only really a small plastic bottle) gets trapped because it can’t get past the gunge. This means that the air pressure is held inside the plastic tube so the pressure switch is jammed ON.

Blocked-pressure-chamber A blocked pressure chamber bottle can also restrict or prevent water getting into the bottle in the first place causing the washer to take in too much water or to overfill.

This would need a fairly solid blockage though and is much more rare than trapping the air pressure as described in the last paragraph. This is because the sheer volume of water inside the tub can sometimes force its way past gunge into the bottle, but because hardly any water actually goes into the bottle this very small amount cannot force its way back out when it drains (if there is a blockage).

If a pneumatic door lock is fitted that prevents the door opening when full of water, a part of the small pressure tubing (at the top of the pressure chamber bottle) branches off and fits onto the door lock. The air pressure is therefore also used to operate a lock inside the door as described in this article different types of door locks.

This type of interlock is rarely used these days because of cost cutting, but it used to be common on washing machines from the 90s. The relevance here is that gunge inside the pressure chamber bottle can also trap air in the tube that leads to the door lock preventing it from opening even when water has been pumped away.

Fixing a blocked pressure system

This article looks specifically at blocked pressure systems and how to fix or diagnose one how to clear a blocked pressure system

Other symptoms

Not taking any water in or refusing to do a fast spin are other possible symptoms of faults on the pressure system related to the machine thinking there is water inside when there isn’t – but as with most of the other symptoms, other unrelated faults can cause the exact same symptoms. General help for these two faults can be found here – not taking in water and not spinning.

Finally, a fault in the pressure system can cause the washer to abort the programme and give an error code – appliance Error codes – What You Need to Know

Get an engineer

Faults on the pressure system can be difficult to diagnose. They can also be very easily misdiagnosed when a fault is caused by something totally different. Don’t just start messing with or replacing parts in the pressure system because your washing machine exhibits symptoms that can be caused by the pressure system. Unless you fully understand how it all works you will be better advised to call an engineer.

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47 thoughts on “Faults on Pressure System”

  1. Andy Trigg (Whitegoodshelp)

    Thanks Steve. It’s unlikely because the pressure switch just waits for a signal as to whether the water is at the correct level when filling and when the water has pumped away during spin. If anything the pressure system faults (commonly a blockage) happen when the water does pump out but the signal doesn’t get through.

    If the water doesn’t drain out fully and needs an additional spin and drain it’s most likely to be caused by a partial blockage in the pump, the pump filter or possibly at the u-bend under the sink (if plumbed into the sink.) Try troubleshooting here –

    How do I clean my pump filter (where is the pump filter?)
    Washing Machine Won’t Drain Water

  2. Hi
    I have moved house and transported the washing machine which is an LG direct drive 8K, the washer has been very reliable, however after installing at my new home and switching it on for its first wash, it started overfilling, the washer normaly uses very little water so to see the drum filling up and not switching off was very strange, it also seems to have stopped detecting load size. Any ideas?

    Thany you

  3. Andy Trigg (Whitegoodshelp)

    Hello Richard. As this fault appears to have been introduced by moving it (which is unusual) you’d have to check that the thin pressure tubing hose is connected OK to the pressure switch and the pressure chamber although I can’t imagine how they could have come off even if you’d thrown it down the stairs. Alternatively maybe there’s a blockage in the pressure chamber bottle and not using it for some days has allowed it to solidify. If you can’t see anything call an engineer.

  4. Our washing machine shows an error code mid cycle which prevents it draining. Through trial and error we’ve found that it will work if the pipe isn’t connected and it drains into the sink instead. Do you think this is a problem with the pressure system or something else. We’ve just moved into a new house and this is only the second time we’ve used the machine which was in the propert already.

  5. Hello!

    I’d just like to thank you for this article and will leave my experience here to help any others with this issue. I have a samsung washing machine that started to give a 5e error. I checked all the obvious stuff, like the filter and blockages in the drainage plumbing. However when initiating a cycle the machine would simply run the drain pump until it timed out and gave 5e again. I removed the detergent drawer and stuck the garden hose in there to manually fill the machine and check if the drainage system was working, like and behold it was pumping out all the water I put in perfectly. After reading your article I thought I’d try the presssure switch, I simply removed the tube from the pressure switch and tried again, boom, working fine. Clearly there was a blockage at the other end of the tube. I blew down it as hard as I could and felt something give, probably a nice mix of soap scum, scale and other debris that had formed a a bung in the tube. Also (very carefully) forced a couple of gob fulls of water down it to make sure it was clear. I blew down again regularly over the next hour to dry it out. Put the lot back together and all is working as it should. So the Samsung 5e error can indeed be caused by the pressure switch system. Certainly worth checking before a call out.

    Thanks again!

  6. Andy Trigg (Whitegoodshelp)

    Thanks Fred. Just bear in mind that clearing a blockage in this way is more often than not only temporary. Just keep an eye on it in case the fault comes back. Blockages in the pressure system can also cause an appliance to overfill.

  7. Hi, I have a samsung ecobubble 2013 washing machine, model no WF1602W5S, I keep getting a sud error code even when I wash with no soap in, I have checked the filter, drain pump, & have taken off & cleaned out the pressure pipe,I have reset the machine, but still get the error code, could you tell me if the foam sensor is part of the pressure switch, or is located elsewhere in the machine, I have been on to Samsung, & they cant help.

  8. Andy Trigg (Whitegoodshelp)

    Helo Paul. This “error” is supposed to clear itself. If it doesn’t, the advice is to run either an “Eco drum clean” cycle (only available on some models) or a 90°C cotton cycle with no detergent or washing load.

  9. Hi, I have a Bosch front loader with a tricky problem and hope you may be able to offer a solution. I have been an appliance repairman for some 15 years and have never seen this before.
    The machine overfills on every cycle and when pressure switch closes on its first notch, it begins the wash cycle. However it will continue to fill until the drain pump activates on the second notch, and when it reaches its normal water level the inlet valves close. This happens on every fill stage.
    On occasion and intermittently, the water valves will re-activate on the wash cycle, sometimes getting a few pulses of power to the inlet valves.
    I suspected a fault in the control PCB, so I switched it out for another from another working machine and got the same problem.
    The pressure switch and inlet valves are working normally and I have checked for any other pressure systems abnormalities-none found.
    The machine is not syphoning and has no leaks.
    The bizarre thing is, that when it activates pressure switch on 1st. notch; if I turn the tap off and immediately turn back on again, the water stops.
    Can you shed any light on this?

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