Carbon Monoxide?? Should I sue?

My husband and a builder did some investigate around our chimney this weekend and discovered that there was a 2nd channel leading from the chimney to under our floor boards. This is coming from the chimney for a solid fuel range in which we burn coal and turf. This has only been discover 3 years after we build our house which we had not 1 but 2 engineers overseeing the building of our house. My 6 year old daughter has been in hospital numerous times with supposed viral infections. I suffer with chronic headaches which only started when we moved into our house. Do you think we have a legal case?