As with virtually any car, Centos can suffer with overheating, but our little cars run quite hot anyway - it's normal for the cooling fan to cut in and out every 30 seconds or so when stuck in queue traffic. Here are a few possible causes.

Loss of pressure in cooling system - the water needs to be pressurised to raise its boiling point, otherwise localised boiling can occur inside the water passages - this can be caused by leaks or a faulty expansion bottle cap (£3 from Halfords).

Sadly, radiators don't last too long either, average 4 years or less, you can have the tiniest of pin holes which can be really difficult to locate
If the little cooling fins are rotten or missing on the radiator, the efficiency will be greatly reduced and can also contribute to overheating.

Electrical failure
The fan switch or fan itself can fail, robbing your car of that extra air flow over the radiator.

Muck! It could be in need of a radiator flush.

Failed thermostat - about £12 each, when they go they can stick open (at least you'd still be able to drive home) or closed (it'll boil over).

The Dreaded Head Gasket - see other post.

Excessively low oil or water levels. (e.g. way under the min mark)