We were recently called out to Elaine's house to repair a leaking toilet. Straightforward enough and a nice simple job, which was accomplished in a very short time.
While there, Elaine asked me to take a look at her oven as it wouldn't light on the piezo spark, but had to be lit manually. On opening the door, tell-tale traces of soot indicated that the device may have been producing carbon monoxide. On testing this, I stopped the CO meter at a reading of 91 parts per million and ventilated the area. The maximum permissible CO emission is 30 ppm, and a reading of 91 is certainly high enough to present a threat to health.
Elaine agreed to have the oven disconnected from the gas supply to avoid any further danger. As a Gas Safe Approved Engineer, I was able to do that for her on the same visit, saving time, money and inconvenience.