Thought I would take some pics as I did mine this morning.

The problem
The main radiator fans do not kick in. My aircon is always on so my temperature only used to get up to 98/99 deg. Still too hot!
Thanks to TB for diagnosing it  

The fix
A new fan switch for about £32 (possibly less with less TC)

Required:
10mm spanner for the battery terminals
Pump pliers or molegrips for the hose clip
30mm combination spanner (preferably a deep socket) for the switch
Oil catch pan
About 3l of premixed coolant

Health & Safety
Do not do this with a hot engine! I left mine to cool for the time it took to cook & eat a bacon butty
Regs mean you should dispose of used coolant properly. Down the toilet is probably OK. Down a rain drain is not.
Do not leave puddles of it on the floor. It tastes good to cats and can kill them through kidney failure...

The job.
The fan switch is on the left hand side of the rad (viewed from the engine). Bits removed for clarity.



This job is ideal to combine with a system flush. Instructions here:
http://www.omegaowners.com/forum/YaBB.pl?num=1167917774
My coolant was still nice and clear so it can wait for the upcoming cambelt change.  

Remove the cap from the expansion tank.
Remove the battery.
Pull the clip back and pull the top hose off the rad. Expect to loose 1-2l of coolant.




Here is the fan switch. Mine has the rectangular connector. Some are oval...




Remove the fan switch. (The electrical connector has a push spring clip on it).
You will loose another 1-2l of coolant.

Clean the sealing washer and sealing face on the rad.

Fit the new switch. CARE - It doesn't need to be much more than hand tight. Don't swing off your 30mm spanner

Re-fit the top hose.

Re-fit the battery.

Top up with premixed coolant.

Burp the top hose (squeeze it to remove any trapped air)
Run the engine up, burping the hose as you go.
Replace the expansion tank cap before fully warm.

JD
Fans now cut in just above 95 deg.  


Keep an eye on the coolant over the next day or so in case it needs a final top up.