All new central heating installations have to comply with Part L of the building regulations. All new boilers have to have a minimum SEDBUK rating of B and A rated is preferred. For a boiler to meet this criteria it would be a condensing boiler, Any work done has to meet these regulations including re-siting an existing boiler. Also under part L you have to have the minimum standard programmer and room thermostat to control the system or better still a digital programable room thermostat. This gives you lockout protection and stops the boiler from cycleing. Then also you need individual Thermostatic Radiator Vales for each radiator you have with the execption of the radiator in the same room as the room thermostat. This is the only way you can now meet the regulations. All gas appliances require a carefully calculated pipe size big enough to deliver the required volume of gas to run safely and this may include having to upgrade the whole installation of pipes so that other appliances are not affected aswell. The majority of band A and B boilers need a minimum 22mm gas pipe.