Your boiler is not fitted to manufactures instructions due to *incorrect positioning* of the flue, for this reason your boiler has been damaged, flues on standard efficiency boilers must *run away from the boiler* to stop rain water and condense from flowing in to the combustion chamber, once a boiler has been damaged by fluids getting into the combustion chamber it becomes hard to determine the extent of the damage to the components on a boiler, I would down load the installation instructions for your boiler which tend to be idiot proof if looked at, then read out loud to the builder and the builders plumber to educate them on the correct installation procedure for a boiler flue, also ring the manufactures and see if they can recommend a engineer to write a report, at the end of the day it's not the opinion of any gas fitter but the black and white instruction in the manufactures instructions manual(backed up by IS813 Irish standards) and as a manufactures technician it kills me to say the Bord Gais engineer is spot on, good luck, Gary