Engine fan permanately on

[Graham Gathercole]

Hi        Recently the engine fan on my Astra comes as soon as I start engine and stays on until I switch the engine off. Can anyone tell me why please.  Secondly, I recently had  a replacement  leaking engine hot water pipe. When I left the car it had a mileage of 110,000, when I got it back it showed 178,000. I spoke to the mechanic he told me that he had not been anywhere anything that would cause this. What do I need to do now? 

[Doc.]

You may have found the cause by now, but if you have the Air-Con switched on, I'm fairly sure the Fan will run continuously.