Its either your microswitch or diverter valve. I would recommend changing your microswitch first as its the easiest and cheapest part to replace. This is the one you require:
http://cgi.ebay.co.uk/RAVENHEAT-LITTLE-STAR-LS-0012NIC09010-0-MICROSWITCH_W0QQitemZ200299664373QQcmdZViewItemQQptZUK_Home_Garden_Hearing_Cooling_Air?hash=item200299664373&_trksid=p3286.c0.m14&_trkparms=72%3A1301|66%3A2|65%3A12|39%3A2|240%3A1318
Joe
January 2009