if it a issue like this dont spend money on guessing what you should do is use british gas as the charge a one of fee or £140 to non members which inc parts and labour for any fault. they come out first check and if they cant fix it no charge i know its not much help now but maybe in the future and i be guessing with out seeing in and soldering the pcb does not mean it not faulty i would advise you phone alpha as all boiler company's have a technical help line for installers and repairers and they know better than any engineer they helped me find faults like these and they will go through a fault finding and testing procedure best to have your mate the engineer around as it does help to have someone in the know
kash
September 2010