i have an electric shower in each house we have lived in cos my sisterinlaw has a combi with this so called benefit of no stored water and all the massive space of an airing cupboard given back to them when the combi was installed.every time it breaks down they have no hot water for washing, last time was 4 days so in the end they went up the local swimming baths on a sunday morning, �10 for 4 showers
my point is the electric shower is an alternative and with older heating systems/boilers you have a source of instant hot water