A good friend of mine who is a heating system installer / repairer can speak highly enough of Viessmann! Best by far!
http://www.which.co.uk/home-and-gar...mann boilers&gclid=COfY77S1pLwCFQrpwgodGDgAlQ
http://www.which.co.uk/home-and-gar...mann boilers&gclid=COfY77S1pLwCFQrpwgodGDgAlQ