fan problem on potterton promax 24he?

i have a potterton promax 24he condensing boiler.the problem is with the fan.on starting the boiler the fan should start first and then the boiler lights.my problem is that the fan does not allways start.
i looked at the fan and noticed that if you give it a little push it will start,but when turned off,depending on where it stopped it will not start again.the fan is a 24vdc brushless type.
if you can imagine the four magnets in the fan,it will only start when it stops in between two of the magnets.if it stops in between the other two it will not start.
is the fan faulty or the circuit board.
thanks Darren.