Hey guys, thanks for the replies.
So if I'm understanding this correctly, if I turn on the car heater the main fan will come on? When I turn on the a/c the left fan comes on, I have LHD, don't know if it matters.
Right fan I have not seen come on for ages.
Is this correct so far?
As far as air pockets, I've had the coolant drained and replaced a month ago at the shop, it's been doing the overheating before that.

I'm really, REALLY hoping it's not the head gaskets, I would hate to have to pull the engine...

R.