Part L of the Building Regulations for England and Wales and Part J for Scotland, relating to the performance of gas and oil fired hot water central heating became law on 1 April 2002, and for the first time the Building Regulations applied to work on existing as well as new domestic central heating installations ( excluding Scotland ). The regulations allow for the alternative use of the Good Practice Guide ( GPG ) 302 published by BRECSU. New installations in properties with a floor area up to 150 sq m must be fully pumped and have independent time and temperature controls fitted to the heating and hot water circuits, and the heating circuit must have at least two zones, with the main zone being thermostatically controlled, and the other zones similarly controlled or the radiators fitted with thermostatic valves. A boiler on/off interlock must also be fitted. Similar requirements apply when the boiler or the hot water storage cylinder of an existing installation is replaced. The Association of Controls Manufacturers ( TACMA ) has produced a free four page guide to assist with compliance.