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 multiple times and then eventually it does light successfully. I assume that some part is wearing or on the point of failing. Maybe no spark being generated? I certainly can't see one through the viewing window, but maybe you can't see one anyway.

Any ideas?