my potterton profile 80 keeps cutting out?

How can I fix my Potterton Profile 100e?

Although my Potterton Profile 100e boiler is working, there are symptoms which I fear could indicate that a problem is brewing.

When the boiler tries to light, I hear a fan, a few clicks and then nothing - the fan noise stops. This is repeated up to 15 times and then eventually it does light successfully. I assume that some part is wearing or on the point of failing.
Any ideas?