I have seen a company on line who offer a repair service for boiler PCBs. It's an exchange service though - you send yours to them and they send one back. I think the cost is about one third of a new one. Try here...
http://www.cetltd.com/
Or do it yourself...
http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler
Good luck...
Peccavi, May 2009