Just so others can learn from my mistakes!
Maybe almost two months ago (when it was still relatively warm) I noticed my thermo fan wasn't working, so I checked the fan by connecting it direct to the battery and it worked. Logical assumption, the thermo fan switch (the one which screws into the radiator) is buggered, so I replaced it.
Last night I was sitting at the traffic lights for a bit and noticed, the temp getting up then I checked and the thermo fan hadn't kicked in, WTF!? Logic told me it shouldn't be a dodgy switch again, so I went home and checked the switch that I had replaced (I don't throw anything out) - I checked it with a globe, wire, battery and pot of water on the stove. The switch was okay!
I then puled the bike apart a bit and checked for a broken wire, but all the wiring was good, again, WTF!? Looking further I found the radiator was low in water, so topped it up, only took about a cup, but that was enough to make a difference and let the thermo switch work. So basically I blew $40 because I didn't check the part I was replacing and also failed to look at the simplest things first.
Hopefully this lesson can save someone else some money and effort!