as far as im concerened we give customers the low down on what is needed to bring a system up to part L standards.we give a written estimate of what the extra cost is gonna be .end of the day its up to the customer.you cant force them to pay for extra work when the system has worked perfectly well for previous years.what next, its illegal to fix a back boiler cos it aint efficient.
no, ya just turn the back boiler off cuz they haven't upgraded the ventilation