I thing we will go for Bosch GreenStar 35HE - expensive but we're looking for quality and reliability, efficiency and economy.
I believe Bosch has all that, please correct me if i'm wrong.
Many Thanks
THE SYSTEM
The Worcester Bosch CDi Combi is a sealed system appliance with an integral expansion vessel, pressure gauge and safety valve.
PERFORMANCE
Modulating outputs to central heating - 9 - 24kW (30,700 -82,000Btu/h) on the 24 and 28CDi models and 9 - 25kW (30,700 - 85,000 Btu/h) on the 35CDi. Domestic hot water flow rate:
24kW version 9.5 litres per minute (2.1 gallons per minute) at 35deg. C rise.
28kW version 11.4 litres per minute (2.5 gallons per minute) at 35deg. C rise.
35kW version 14.3 litres per minute (3.2 gallons per minute) at 35deg. C rise.
FLUE OPTIONS
The 24CDi is available in three fluing options - OF, BF and multi-directional RSF, whilst the 28CDi and 35CDi models are available in RSF versions only. The 28CDi RSF system can be run both horizontally and vertically, with the option of 45deg. C and 90deg. C bends. Anti-cycle control The CDi incorporates an anti cycle control system which, when used with heating systems with thermostatic radiator valves, eliminates wasteful 'cycling' of the boiler.