Set Square wrote:
In an earlier contribution to this discussion,
Kate11171 wrote:

We are having trouble finding a plumber to install a combi boiler for
us. My husband is quite confident that he could do the job himself but
obviously it has to have a certificate from a CORGI registerd plumber.
Do you know if it is possible or legal for my husband to do the work
and a plumber come in and inspect it and pass it or would a plumber be
reluctant to do this?
Thanks

It's perfectly legal. How easy it is to get a CORGI to certify someone
else's work, I don't know. I guess that the CORGI would want to do the gas
installation and commissioning himself - leaving the physical installation
and the water side to your husband.

There is nothing in law to say CORGI has to get involved at all.
The relevant gas legislation just says "a competant person", if it's for
domestic installation, and not done for gain.
However, the insurance/mortgage/landlord/... may require CORGI testing.