“After the first incident, officials could find no elevated levels of CO in the apartment. The new boiler checked out fine. After the second incident…Norwich Public Utilities, the city Building Department and the Yantic Fire Engine Co. No. 1 combed the apartment, turning on each appliance and checking…They discovered the gas stove had a hidden flaw — a clogged gas nozzle — that caused incomplete combustion as the oven was operating.”