Hi, mine is the same. From what i have read, it is the resistor on the blower fan. The circuits to make settings 1,2 + 3 work are on the resistor that needs replaced. The reason it works on setting 4 is that there is no resistor, as setting 4 uses full voltage. Obviously 1 ,2 + 3 are on resisted circuits to cut the power going to them, making them obviously less powerfull.
I am going to fix mine tomorrow. I will take some piccys if i remember. i have been quoted £16 + VAT for the resistor which i think i quite high but i am going to get one tomorrow. I will post my findings 8)
Good luck
Rob (Bobster)