Skunkworks11

Hi everyone Car is Octavia 1.9dti mk2 2010. Fault started about 3 weeks ago and has steadily got worse. Fan would come on and off randomly during journey whether engine was hot or cold. it now comes on within 5mins of starting and runs the whole time, only stopping when i turn ignition off and you cam hear fan slowing down. From reading other post i believe there is 2 temp sensors( 1 engine water temp and 1 on radiator) and a fan controller My question is, which one is most likely to be at fault with the symptoms I'm getting ? Thanks in advance