Cooling Fan Not coming on after switch change

Sooo I had a radiator fan switch (2pin) fitted that was working fine but the plastic was old & broken away badly so i've decided to change it for a nice new one (Topaz).
I've tested the new switch in a pan of hot water before fitting just to make sure its ok from new. It is working fine.
Fitted it and now the fan isnt coming on and after long idle the car boils over.

My thoughts are its a possible air lock in the rad causing this?? No other air lock type problems.
I've pumped the hoses for abit and had the header cap off etc so i would of thought any air would of come out..

Thoughts people??? Cheers

Yes, but then did you verify that there is 12V on one side of the new switch?

Are you sure that if you jumper your motor to ground and the battery it comes on?

When you filled the thing did you fill from the upper hose to the engine, then the upper hose to the radiator?

1st unplug the fan switch and loop a wire between the pins, if the fan runs then switch is bad or coolant isnt circulating round the rad properly.

if fan doesn't run check fan fuse, check you have 12v on the switch red wire and a good earth on fan brown.  As Briano says jump the fan with 12v direct from battery to make sure its working

when running the engine with the cap off you need to make sure to put the cap back on before the coolant starts to boil otherwise you'll end up with a load more air in the system. check the cap seal is good too

when running the engine up from cold the lower hose should stay stone cold till the gauge gets to about 1/2 then warm as the stat opens, then fan should cut in around 3/4