I've recently inherited a 2002 Focus from my parents, who mentioned afterwards the NS footwell gets wet if it rains.. Here we go I thought...

Yep, you can guess what happened next, fan speeds 1-3 dead !

Long story short, Google turned up this thread with excellent info on diagnosing and solving the issue. So I then confirmed the thermal fuse was open circuit.
Have now ordered replacement pollen filter/seal and the redesigned scuttle cover to solve the root cause. Will source new fuses from Maplins nearby.
Now going to remove the fan motor to check bearings and lubricate. Will post an update later.

I am new to maintaining vehicles, but eager, and with the absense of anyone mechanical to "hold my hand" I've ordered a haynes manual - pls don't laugh!

I certainly wouldn't have known where to begin without the help you have posted here, so I just wanted to say a big THANK YOU and also HELLO for my first post.