You do not say the boiler details - just PCB
You may not need a circuit diagram
They commonly suffer broken down electrolytic capacitors and dry joints
A digital photo will give you confidence when you come to put it back together
Here's a link to a pcb repair on a Potterton Profile...
http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler
Good luck...
Peccavi, January 2010
