I think the real issue here is the competence and professionalism of the heating engineer. Clearly a fully competent engineer who does his best to diagnose a problem but is unable to, at least within a reasonable time, due to the obscurity or intermittency of the problem, nevertheless deserves to be paid for his time.
I don't think a reasonable customer would really mind paying up either, if he was confident that the engineer had applied a good standard of competence, knowledge and experience to diagnosing the problem, although in many cases the engineer may only ask for a reduced fee as a goodwill gesture.
But there will always be a suspicion in the mind of the customer that failure to diagnose is a sign of incompetence. And it's clear from many posts on this forum that there are many incompetent "heating engineers" out there, so such a suspicion is far from groundless.
I don't think a reasonable customer would really mind paying up either, if he was confident that the engineer had applied a good standard of competence, knowledge and experience to diagnosing the problem, although in many cases the engineer may only ask for a reduced fee as a goodwill gesture.
But there will always be a suspicion in the mind of the customer that failure to diagnose is a sign of incompetence. And it's clear from many posts on this forum that there are many incompetent "heating engineers" out there, so such a suspicion is far from groundless.
