I read recently that certain engineers are getting upset about others entering boilers...Do you change your look at your tyres, lift the bonnet /open /view the various caps to check levels or change your brake pads? Some of us have far more common sense than the average plumber/gas engineer..The guy Chris who's blog i read was well competent in what he was doing...The problem is there are a lack of good honest gas fitters who are available and the others with no common sense and only a certificate seem to come out of the woodwork in times of need. I have a good engineer who does my properties when I cannot find the obvious. But there is no reason why an electrician, an electrical engineer or even a car mechanic cannot investigate......