There is a case with storage heaters, where some models retain the energy until required better than others. And heat pumps are more efficient to simple resistive. And some controls are better at reducing the hysteresis as heaters turn on/off.
But the EPC rating using some really odd ways to rate a property, due to the way it is banded, it can be 10 to 20 points between each band, and one has to look at if one can get into the next band for a reasonable outlay.
So my house would need 11 points to get into the next band, some things have already been done, but I have a leeway of 1 point. So first 2 points is it seems floor insulation, at £4,000 - £6,000 to gain £48 a year it is a non-starter. Do everything else on the list and I still will not get into the next band, so to get into next band, simply it's a non-starter.
Since the survey, all bulbs now LED, and solar photovoltaic panels 6 kW fitted, so there is no room to fit solar water heating, and it would be pointless, as the solar photovoltaic panels also heat the DHW. All the double glazing has been changed to units which are better rated, half the loft floored, the other half extra insulation added, and the central heating controls have been improved, but none of that was on the list.
My yearly electric bill is around £300, but they are not interested in that, so I still with all the improvements have not got onto the next band.
There is a flat under the main house, and it says "Hot water from main system, no cylinder thermostat Poor" Well there is and always has been a cylinder thermostat to control the immersion heater, and since the immersion is heated by excess solar I would have thought it should say very good, but don't even know why it is listed, as the cylinder is not even in the flat, it is in the main house.
For the main house it also says "Hot water From main system, no cylinder thermostat Poor" I have never seen any immersion heater fitted without a thermostat, and it is both cheaper (when one has solar panels and also likely without them as well) are more energy efficient, as no losses with electric, to use the immersion heater rather than the oil fired central heating.
So in real terms one can forget the EPC as it is simply not linked to real life.