The Worcester Bosch Greenstar 4000 18kW System Gas Boiler is a condensing system boiler for medium homes with up to 12 radiators and 1-2 bathrooms, requiring a cylinder. It delivers an 18kW output and a 94% efficiency rating (ErP A-rated). Measuring 710x400x330mm and weighing 33kg, it fits cupboards. It features a 1:10 modulation ratio, a stainless steel heat exchanger, and EasyControl. It supports natural gas and offers a 7-year warranty, extendable to 10 years with a filter and Excelerate installer. Great for family homes.