sooey said:It makes it non compliant, unless you have a pretty unusual home. A lot of non compliant boilers were fitted back then in places they shouldn't have been, usually on the cheap.
and then OP asked Can you please explain more please
There were exemptions to the rule that a new boiler must be a condensing boiler. It worked on a points scheme. Most houses started with about 600 points and extra points were added for things like difficulty in installing a balanced flue. If the points added up to 1000 then a non condensing boiler could be fitted.
Points were added if the radiator system would need to be changed to allow the condensing boiler to operate in condensing mode.
In many cases larger radiators were needed due to the lower circulation water temperature necessary for the boiler to operate in condensing mode. Even today there are condensing boilers that operate for long periods in non condensing mode due to poor system design requiring high temperatures in the water circulating through the under sized radiators.