... or is it a case of "if you can't write a helpful reply, then you
shouldn't"?

I was merely responding directly to the question. The nature of the question
and surrounding text led me to the opinion that the OP would not be
considered competent to service gas appliances. Unless, of course, you
define "helpful" as saying "yes, of course, go ahead", rather than giving an
honest opinion based on the facts that are known or can be deduced, which, I
suspect, the OP would find rather more useful.

Christian.