Had gas furnace serviced (routine yearly) and was told the heat exchanger was cracked and might pose a CO problem. System shut off and tagged. Told I needed to replace exchanger or get new furnace. Got second opinion next day and they found no CO and said previous check (other company) couldn't diagnose cracked heat exchanger so easily (said it takes a variety of tests to diagnose). They couldn't find anything obviously wrong with furnace, checked CO levels 4 times over approx. an hour, all normal. Should I get a third opinion?? Think first company was pulling a scam? Furnace is 16 years old, but want company I can trust....ugh Liking second company. Any opinions? Thanks!