Avoid the "Combi Cowboys" and get 400 Boiler Trade-in Scheme Discount on Worcester Bosch Greenstar Combi Boiler Installations. With more than 1 million Greenstars already installed, the award-winning boiler series is already well-established in the UK. The all new Greenstar gas-fired Si Compact is ideal for tight spaces which enables the appliances to deliver DHW flow rates of 10.2 and 12.3 l/min despite their compact size. Greenstar CDi Compact combi boilers are the smallest and most efficient boilers Bosch have produced.