Dishwasher pressure switch

Hi,
I have a belling 603 dishwasher and keep getting the e1 fault.
Sometimes it starts the cycle and after a few miutes comes up with the e1 fault and other times it leaves the bottom full of water.
Last night at the end of the cycle it carried on trying to drain even though the bottom was empty.
Ive taken off the pressure switch and the pipe and switch are full of water.
Is this the way it works or is there something wrong here?
Hope someone can throw some light on the matter.
many thanks steve

The pressure switch is usually mounted above the height that the water gets to inside the washer or there is a loop of pipework going above the internal water level.

Water enters the pipe forcing the air up the pipe until it is compressed enough for it to operate the diaphram on the pressure switch.

So there is usually some water in the pipe to the pressure switch, the switch itself should not have water in it.

Occasionally the switch or pipe work moves or falls down (or water gets in when it is moved ) allowing water to enter the switch and operate it or short it out. This will cause the machine to constantly think it is full and try to drain.

You can test it by disconnecting the pipe from the pressure switch and keep the pipe up as high as you can above the internal water level. Fit a pipe onto the pressure switch and blow into it (with the power off) you should hear some clicks.
With the pressure switch fitted in its correct place and your extra pipe fitted allow the machine to fill for a short while. Blow into the pipe you fitted onto the pressure switch till you hear the first click (do not touch the pressure switch) and it should stop filling (you may have a two or more position switch so if you blow harder the drain pump may operate as the machine thinks it is overfull. Allow the pressure in the switch to release and the machine should start filling again.

Drain machine switch off power and re assemble.

Thanks leccy, That was a great explanation.
When I did what you said the dishwasher starting filling,stop filling and draining like you said.
Now ive put the tube from the sump back on its not filling and coming back up with the e1 fault. Could this now be the float switch?
many thanks for your help.

Now when i put it on it just constantly tries to drain even though there's no water in the bottom?

The appliance could have a blockage in the machine - usually on the side of the machine you have a water metering tank it can get crap backfilling into the tank and causes the machine to overfill this can leak into the base and cause the float device to activate and the machine then goes into a drain cycle and doesnt stop until the base is emptied

the float switch is activated by a polestyrene block check it isnt pushing up on the switch