Can't be specific about the Asko machine, but most machines work the same for water level sensing. Unplug the power, pull the top off, and after having a look around the inside you should find one or more narrow rubber tubes (1/2" max dia) leading from near the bottom of the drum to a plastic pressure switch mounted very near the top of the machine. As the drum fills, water goes up the tube, air is pushed ahead of it and pushes against the pressure switch. The switch will be round or square, about 2" across and mostly about 1" thick apart from connectors. There will be two or more wires connected to it. You do sometimes find them siamesed with 2 or more sensors in one unit, but it is rare.
See item 531 on page 4 of this PDF:
http://www.americanappliance.biz/PDFS/ASKO-Washer/W640%20(WM55).pdf
Reasons why they stop working are either that the hose is blocked or crimped, or that the sensor has failed. Should be very easy to diagnose which. As the switch is operated by very small amounts of air pressure, you can just unplug the hose from it, (don't drop the hose as water will drain out if the end falls too low,) and blow into the switch. You may well hear it click, although some of the modern ones are silent. Put a meter across the terminals while you're doing it. If it doesn't appear to be either of those, then you probably need an engineer...
Ed Vine, June 2009
