ZR fan seemingly not kicking in. Any suggestions?

[Nic jones]

Now the hot weather is here I would have expected to hear the fan going when stuck in traffic, but it doesn't seem to be kicking in at all.

The temperature gauge is sitting at just under/on halfway and doesn't go right up, but if you crack open the bonnet it does seem bloody hot in there!

The fan kicks in if you remove the temp sensor from the elbow just below the water pipe (on the gearbox side of the engine near the top).

I've also checked all the fuses, and they look fine, could it be the relay in the engine fuse box?

It doesn't seem to be causing any problem with the car as such, but obviously if I do get stuck in a traffic jam I don't really want it overheating!

Thanks