Boiler is in an outside cupboard, flue consists of a 90 degree bend to the left and then straight through the outside wall to the terminal - no more than 2 feet long. when the landlord's heating guy first looked at the problems and spoke to Viessmann technical there was a suggestion that there were now modfied parts available for the flue (boiler was installed May 2005). I can't see any sign of any part of the flue having been replaced during the recent visits - are there modified parts for the flue?