The short answer is no.
You must be fully qualified just to hang the boiler.
I beleive it is also now illegal for a non qualified engineer to remove the casing on a boiler with an open burner.
You must be competent to do any work on any gasappliance.
Not strictly true though is it.
As far as i am aware you may disconnect and reconnect the same bayonet fitting if you wish.
Hi , It,s me again. The reason for my request is I have just had a qualified engineer out from 1 of the big companies to locate inermitant fault causing pilot light to keep going out, it is under contract.after 1.5 hours he left with no idea what the problem was, he called out transco as he maintained gas pressure was low, and left several screws out. his attitude was awful, the pressure was spot on, transco checked it. still have the problem:
Connecting and disconnecting a cooker bayonet is not considered working on a gasappliance.
They are specifically designed to make it possible to move a freestanding cooker so you can clean behind and underneath.
That leaves in place that you need to be competent to work legally on any gasappliance. An electrician who connects the power cable or controls to a boiler is deemed to be competent to do that job. He would probably be deemed competent to change the pcb. Changing the gasvalve becomes questionable.
When the op installed the boiler 15 years ago, and it has worked this long without hurting anybody, it can be argued he was competent on the job he did then.
Corgi technical bulletin 214 made it clear they did not agree with RGI's signing off other people's work.
We will have to see what crapita's position is on this now corgi have become a plumber's merchant.
I wouldn't put it past them to make a special exception license available at £xxx