I recently had 'replacement' Windows (PVCu) and a front door fitted by
a FENSA registered company. The windows were fine but the front door
leaks like a sieve as is does not completely mate with the seals
either outer or inner. The simple reason is the door is slightly
'warped

Obviously I am in 'dispute' with the supplier to replace the door and
that is another story!

What I am particularly interested in is the 'self certification'
aspect. If I understand the response to a question to FENSA on this
issue, FENSA are only interested in the 'design' aspect, that is that
the replacement parts meet Part L of the Building Code (I think that
is right). From their response, FENSA apparently couldn't care less
if the components are fitted correctly to ensure they are air tight.

The local Building Inspectors tell me they thought FENSA self
certification also covered installation, that is the installed product
is air tight and meets the intent of the code.

Anyone with any insight on this?

Referring to the installation, the 'fitters' simply installed the door
and windows. There was no check by anyone to ensure the parts sealed
when closed, no 'Quality Control' and on the basis the door was warped
before installation no or ineffective Quality Assurance. It seems to
me this FENSA self certification scheme is little short of a marketing
scam.

What particularly annoys me is how many other installations are
similarly defective? I checked the seals but how many do this? Not
many I suspect.