How to Fix 'Radiator Fan continues to run when Ignition off issue'.Citroen C4 GrandPicasso(2006-13).

Radiator Fan keeps running after engine is switched off.
Open the door the radiator fan turns on and stays on.
Eventually draining the battery, no faults/alarms on screen.
After trying many fixes, changing coolant, looking at the particle filter for blockage perhaps?
We found the fan control unit to be the culprit and here's the fix that worked for me.
EDIT/UPDATE.
Well, the issue returned on the 5th day..?!F... So for the last 4 days or so, I have been driving around removing the battery connection so it doesn't drain it and leave me stranded. After researching, and calling around, I luckily found a fan control unit (second hand). Swapped it and all is well again. I still firmly believe this is THE fix. Cheers.
Note, I was recommended to NOT use the silicone Spray, please use electrical contact spray for the contacts (not necessary) but I did, and sensor spray for the coil and resistor section, I have not.. yet.
2nd UPDATE, over a week later and Fix still working, in my case I can confirm Fan Control unit was the issue.