Hi as a retired marine engineer who for last 20yrs on land as a boiler engineer mainly commercial boilers I do get a bit annoyed at people complaining about certified gas/oil boiler engineers who every five years have to take time off from earning money (2weeks)and pay approx 3 to 5k to get tickets as well as buying and yearly calibration of analyzers and other testing equipment .yet never complain about. say solicitors who charge you a fortune for work that is usually done by a clerk in the office then signed off by solicitor.As for uncertified work carried out on gas thank God it is now a criminal offense to do ,as I could give you hundreds of examples of of death and destruction caused by unqualified experts.just saying.