an
honest opinion based on the facts that are known or can be deduced,
which,
I
suspect, the OP would find rather more useful.

Seconded.

Thirded! What the OP should consider is how he would feel if an untrained
person did the work and overlooked something that resulted in death or
injury that is far too common with defective gas appliances. It is quite
evident from the OP that his "friend at work" is not competent to do the
work.