Yes it's very easy - a good tip is to take a photo with a digital camera before you take the old one out - you don't need to know what connects where because it should be impossible to miswire things but a photograph will give you confidence in what you're doing.
Here's a link to replacing a Potterton PCB with text and pictures (click on pictuire for larger image) for a Potterton Profile boiler...
http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler
The link also describes a £1.50 "fix" for common problems.
Don't forget to isolate mains power before starting...
Good luck...
Peccavi, May 2009
