Got a new radiator fan switch that will hopefully make my fan work again.
Possibly a dumb question: can I remove the old one and fit the new one without doing a full drain of the coolant?
Thanks all.

 

Yes. Leave the radiator cap on and be quick about putting the new one in when the old one comes out.

 

I discovered why the radiator fan switch isn't working when I checked the coolant level. I couldn't see any liquid in the neck so I poured some in. I heard a drip drip drip...
The radiator has a new dent in it and the coolant is leaking out at that point.
This means I've been running the bike for three days with NO coolant, turning the fan on when the temp gauge approached the red (which it did very quickly).
Thought it smelled a bit 'fried'!
Could I have caused any damage, e.g. to the water pump?
Thanks again.

 

I'd probly be the most worried about the head gasket. Check for cross contamination in oil and coolant, take a sniff from the radiator fill hole if it smells of exhaust gas, other telltale signs are excessive smoking (water vapor in exhaust) and an inexplicable loss of coolant after rad renewal. The only way to be 100% sure would be to pop the head but I'd reckon that shouldn't be necessary unless there is a firm suspicion of a failure. One thing you could do is take the plugs off and crank the engine with the start, if there's water in the cylinders you'll notice.

 

Patched it up with J-B Weld and added K-Seal
Put a new fan switch in
Seemed OK when I revved it up
Will see how it goes next time I ride