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.
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.
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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
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
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.
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.
Mike Crouch says
When I blow in my washer pressure switch it clicks twice bur the pressure leaks out..in fact I can hear a hissing sound when I continue to blow after the clicks….I presume the diaphragm has a leak or perhaps it has an intentional leak. Should it have no leaks?
Thanks
Mike
Andy Trigg (Whitegoodshelp) says
Hello Mike, if it’s one of the old style pressure switches that physically turns switches on and off it should be totally airtight. You should be able to blow into in and place your finger over the spout and the click should hold. You might not be able to get a finger on it fast enough to trap both clicks but should be able to trap the last click which should hold until finger is released. But if you can tell that air is passing though it somehow it must have a leak. If this is the case I would expect the machine to overfill, or to constantly keep topping up with water as the air pressure keeps dropping (which would result eventually in overfilling) or it should abort the cycle with an error.
Keith Grine says
When I start a cycle, my washer automatically starts in the drain mode and does not start filling with water. Would a problem with the pressure switch cause this issue?
Thanks
Andy Trigg (Whitegoodshelp) says
Hello Keith, all modern washing machines tend to energise the pump for a short while before starting a wash cycle. It’s just to make sure the machine is empty. If it fails to fill with water after 20 or 30 seconds there could be a fault with the water supply to the machine or the water valve in the machine (check this article – Washer won’t fill with water
In relation to the pressure system, a fault on the pressure system (as described in this article above) could convince the washing machine it already has water inside and that would stop it taking any more water in. However, I would also expect that if this is the case the drum would start turning as if washing the laundry and it would also refuse to spin.
A final possibility is if by any chance there was a fault or partial blockage in the pump or plumbing resulting in the washer not being able to empty the water out properly although I would expect it to be fairly obvious that there is still some water inside the machine.
Peter Boucher says
Hi Andy, I have a Samsung Top loader (FUZZY LOGIC). As soon as I press the power on button, The cold water solenoid energizes and water is let in. The water continues to run in until the power switch is switched off. I have replaced the solenoid with a new one but still does the same thing. Any Ideas?? I i disconnect the cold water, select a cycle and select only the hot water. the machine works fine?? Your assistance will be greatly appreciated.
Andy Trigg (Whitegoodshelp) says
Hello Peter, it doesn’t sound related to the pressure system. The valve must be getting a live supply and a neutral return from somewhere. Insulation faults can cause weird things to happen. You would need an engineer with an insulation test meter to check it out.
Patrick Lovering says
This sounds like a problem I’m having with my hoover washing machine, It fills for about five seconds then stops. goes through the program with hardly any water in the drum and then stops with an E03 drain problem message. The machine drains well though. I have replaced the water valves to no avail, and there is a good rush of water going in for the 5 seconds. The pressure switch appears to be working the pipe to it is clear, and there is no improvement when the pressure tube is removed. Any ideas?
Patrick
I’ seem to remember having this problem before now, and pressing a combination of buttons to reset the program?
Andy Trigg (Whitegoodshelp) says
Hello Patrick. If you remove the pressure tube the washer should overfill. If it isn’t then I’d suspect the pressure switch though I can’t guarantee it.
patrick says
Ok thanks Andy, yes have removed tube and blown it clear, left it removed but still wouldn’t fill, disconnected the switch and no joy, does it fail open or closed do you know?
Andy Trigg (Whitegoodshelp) says
It does sound like the pressure switch isn’t working properly. The pressure system tells the machine when it has enough water in and when the water has drained away. If it’s not doing either you have to suspect a faulty pressure switch or something’s gone wrong with processing or receiving its signals. This article explains how the washing machine controls water levels.