It may not have been available when you bought the Highflow, but I find the Rinnai multi point water heaters very good. They deliver high flow rates and never run out. You then need a small system boiler for the heating. The Gledhill Gulfstream, which has full electric backup for CH and hot water, can also deliver very high flow rates, depending on which model, as does the ACV Heatmaster, although these are more expensive than the Highflow.