Just get a combi with a good DHW output (scrap all the tanks). The Keston C36 (14.5 l/min), Valliant 835 (14.3 l/min), Ferroli Maxima 35C (14.2 l/min), Baxi 133 HE (16 l/min), Vokera Syntesi 35 (14 l/min), Chaffoteaux and Maury minima 35 (14.2 l/min), Gloworm 38CXI (15.5 l/min), Potterton Gold...