We have a 250 liter mains pressure hot water cylinder fitted 2012, not sure what brand it is I can't find the docs, but it'll be one of the mainstream ones. It has an extra hot water cylinder wrap that is fairly badly fitted because it was difficult to reach behind and to one side. This week I left it turned on while we were away. I found that it was heating for approx 0.6h per day when no hot water was used, which equates to 2kwh per day of heat loss. I turned it off for a couple of days, three days heating was 1h 42m which was 5.5kwh of heating. I don't know what it costs to heat from cold.

Thought that might be interesting.