Guys came back from work put my bag down sat down to stroke the two welcoming pooches and a million licks, long behold the CO alarm goes off constantly. Shot up to see it's not a battery issue so quickly ran around opening all windows and doors to get fresh air in. I kick the dogs and cat out on the front lawn get upstairs to tell my daughter to get her neck out of the window and stay there and not to MOVE.Shut the central heating off then dash down to turn gas off at mains, then got my daughter out in the front. I was second hand with this running around like a Tw@t, I quickly rang Northern gas network emergency line and told them I had CO alarm go off and the guy was outside in 20 minutes. Anyway the guy goes in with his CO meter and states the reading are too high and shut the gas supply to the house. This has never happened to me before but that CO meter just saved our lives. I was light headed and have this mild headache which is shifting with a few beers. Guys test that CO meter if you don’t have one get one please. Tomorrow the boiler engineers are coming for a full strip of this boiler to see what gone on.