A few weeks ago our CO alarm in the basement near the boiler went off and eventually registered 276 (Fire Dept showed 277). We live just outside Anchorage and put the new boiler in as part of a state sponsored upgrade program about three and half years ago. Searching for answers to the problem led me to your site and a post by Mark325i on 12/7/2012. We had almost identical issues except we do have an outside air source in the boiler room. After discussion with the manufacturer and techs from the location we purchased the boiler from we discovered a door modification kit through a U.S. Boiler Co. product safety bulletin dated 12/2/2011. The techs do not feel that this will make a significant difference and feel the issue is that the high efficiency boilers do not burn as hot or as often as the older models setting up the potential for the flue to not draft with specific atmospheric conditions in and outside the house. We have an electronic dampener that has to open before the furnace fires and it is working as advertised. I am curious if there is an additional exhaust fan that could be installed up the flue pipe and/or possibly a CO cutoff gauge that would shut the furnace down if an event was to happen again. The current flue pipe does not meet the new code regarding how far it extends above the roof line but the tech who came out to specifically look at it said extending it would not necessarily help our internal CO issue and could possibly hurt by having a longer pipe exposed to more cold air.