On Sun, 24 Jan 2021 17:43:54 +0000, thescullster wrote:

Does anyone know whether heating system "design" is regulated for
new builds in any way?


Through Gassafe and the Boilers Manufacturers Warranty.

The Housebuilders will have very little input on what the Heating people
put in.It will be a sub contractor who does the heating work, and they
will have that Contract through being the cheapest Tender. All the
Housebuilder will demand is a radiator in each room and a boiler to give
the correct heating characteristics for the house. They will not check
the designs.
The Builder will deny all responsibility for heating faults and design
failures, and point you to the Heating Engineers if there is a fault.