Hi Natalie,
Out WT540 was showing some flashing indicators this week, and I was wondering the same. If you remove the plastic kit plate from the bottom of the machine, you will see the pump filter enclosure bottom right. It's not easy to remove though. It will turn one eighth of the way anti-clockwise, but no further. What you need to do is, with a pair of strong pliars, turn it clockwise first - half a turn or so, and then you will find that you will/should be able to turn it anti-clockwise all the way out. You'll probably still need the pliars though. You will find some water seeping out, so have a cloth ready. You can then remove the curtain hooks, pieces of metal, cotton buds and general fluff. Once done replace the filter and hopefully away you go.
Pete, November 2008