Some heating engineers may warn you not to do this for your own safety - their motivations may be perfectly honourable. Others might say it's illegal for you to mess around inside a boiler case - they will be wrong.
http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler
A digital camera will help your confidence but it's really not needed - you would have to try really, really hard to miswire a replacement PCB - after all, boiler engineers install them all the time so it can't be too difficult.
Good luck...
Peccavi
February 2010