You can have a combination boiler and pipe up an indirect cyl as a radiator. The cyl could be then used in conjunction with its header tank and a power shower. The cyl could be used to supply hot water to bath and upstairs sink whilst sink taps downstairs are supplied via the combination boiler. Not cheap initially but gives back up of hot water services in case of failure especially if backed up with immersion heater or even solar panels
Simple solution is to fit a condensing system boiler and new indirect cylinder.