candy rapido e20 (draining fault but washer drains fine)

Thanks for that MelS. As far as I can see the modern electronic pressure switches work just how I envisaged. That is there is an electric coil and a magnet. The air pressure created by the water causes the magnet to slowly rise inside the coil. The electronics can then monitor the output or resistance in the coil and be able to tell how far up the magnet has been pushed and therefore how much air pressure (and of course water level) is present.

I would still expect them to be a very reliable part, but quite possibly nowhere near as reliable as the pressure switch is that they replaced. As I said before, I can hardly ever remember replacing a pressure switch which in a washing machine in well over thirty years repairing them. They are exceptionally reliable. These modern ones now have small circuit boards, with small capacitors and chips inside which are all prone to potential failure.

I would still expect that the most likely cause of any problem with water levels is likely to be grease crime and gunge blocking the pressure chamber. This would prevent air from getting into the pressure switch, or conversely with some types of less-solid blockages, trap air inside the pressure switch.

Modern pressure sensors have a coil of wire, wired to a capacitor, the magnet moves into the coil which changes its inductance and the frequency they will oscillate at. Some have additional circuitry to make it oscillate, and others would have that on the control board. I would expect them to be pretty reliable, so most likely a blockage somewhere caused by gunk, or limescale.

Here's a video that explains it better that I can

youtu.be/O-0KGbd91_I

Thanks for updates. Modern pressure switches should give varying readings as the magnet rises. I believe they work by monitoring resistance readings as the magnet rises although I've not seen any actual explanation of how they work.

The previous design of pressure switches were just spring-loaded switches that are either on or off. Historically pressure switches have always been extremely reliable parts and I hardly ever remember having to change one.

The most common cause of the washing machine thinking there is water in the drum when there isn't is blocked pressure system. I would also check for this.

Common faults on washing machine pressure system

Clearing a blocked pressure system

hi all just to let you know i had a look at the pressure sensor and it was putting out some strange readings on my scope its failed so £12 part is on its way ill update you after replacing it but after blowing into it pretty hard the washer started to work perfectly fine so its probably a failed diaphragm in the unit

thanks for the reply sorry i didn't see this sooner i didn't et any notification. the drainage pipe runs up from the bottom and up to the top to act as trap and anti siphon then in to large mixing bucket no water moves until you start the program you can see the water pulsing as the pump surges but at no point dose the drum move which is why i think the error is wrong. it drains then fills a little then drains some more but i assume the drum should spin during draining. i get resistance across various pins various phases so i don't think its a brush issue either. You mentioned pressure issue the pump has no sensors its self and from what i can see the drum simply drains straight into the pump and the raised drainage pipe at the rear hold the water in. maybe there is a sensor in the drum to detect water ill have to have a look if its in the drum it must be near the heating element id think.

I work on audio equipment as a hobby/side job so i know my way around electronics but obviously appliances are a different kettle of fish thanks for the help