Radiator fan always on

Hi all, 

I know this has probably been done to death, but...

The octavia recently died a death, completely and had nothing on the dash, and would would not start. 

That has now been fixed, at an exorbitant cost.

NOW, the radiator fan comes on as soon as I put the key in, and doesnt turn off again until i turn the engine off.

No other ill effects, but is extremley irritating as she has already lost my trust, but the wife wont let me change it.

Any ideas?

Cheers