Hi Mike, Google is your friend!
search string: wm72n fault codes
result:
http://www.ukwhitegoods.co.uk/modules.php?name=Forums&file=viewtopic&t=1698&sid=09b5618a8f5080b842720cb1b9fa0cfd
The consensus is that the problem is to do with the machine emptying, possibly timing out that will happen after two minutes. You seem to be in the right ball park, so have a look at the pressure switch as well.
topolino, August 2004