I would suggest that someone has replaced the fan with a non-timer one and connected the permanent live (red) to the fan instead of the switched live (yellow)
One of these in the roof: -
https://www.tlc-direct.co.uk/Products/QUR323.html
Controlled by one of these: -
https://www.tlc-direct.co.uk/Products/QUWS2W.html
I bought this one as my car wheel bolts are very high torque.
Sealey STW905 Sq Drive Torque Wrench Micrometer Style 60-330Nm-Calibrated, 1/2"
https://amzn.eu/6PgJktM