I've tested hundreds of combustion-fueled heating appliances, and this is way more common than you'd hope. Watch my friend Wade Thompson of Utah's amazing Intermountain Weatherization Training Center give a quick demonstration of how easy it is to pass and fail this important home health test.
See way more about Wade's work in Season 2 of Home Diagnosis: https://HomeDiagnosis.tv
Check out Wade's organization: http://iwtcutah.org/