Flat battery - fan staying on !!!

I have had a flat battery twice now in less than a week and i have now noticed that the cause is that the fan (situated under the bonnet in the middle of the bulkhead) is staying on. I have tried taking out all the fuses in the drivers footwell one at a time to switch it off, but to no avail and have now temporarily resorted to removing the negative battery terminal in order to stop the battery going flat. please can someone point me in the right direction to resolve this.

Many Thanks Andy