I had the usual problem of the fan not working on speeds 1 & 2 and remember reading somewhere ages ago that instead of just changing the resistor pack (?15) you can change the thermal fuse (47p).
Did it today and it worked !!
All you need to do is take the resistor pack out the side of the blower, snip out the thermal fuse and replace it.
I changed the standard 182 degC one for a 220 degC