Run of the Mill Boiler, prone to niggling faults, at at 80,000Btu, may struggle to proved good hot water in winter when the rising main is Cold!
Personally I would not fit a combi of 80,000 Btu
120,000 is a better bet, I wouldn't fit a Potterton
Try a Broag - Remeha 35c
www.elanar.co.uk, September 2009