Having read the article , whilst broadly accurate it is misleading in respect of the use of a flue gas analyser.
Fact is that the AWS does NOT require the use of a flue gas analyser, and a room test for CO is not a requirement of the AWS service sheet.
A good engineer will have taken on board the issues that I personally have raised and promoted about the use of Flue Gas analysers and will use one to not only do a room test but also the exhaust from the heater, cooker, and any other gas burning appliance.
Just turning a gas appliance on to see if it lights is NOT good enough and I would urge users to demand the readouts from the Flue Gas Analyser (which would automatically be given by a GOOD engineer) for each appliance.
If your choice of service agent does NOT do this essential testing, do you want to rely on his word alone.........I don't !!!!