Soldato
When I had my old cylinder I would turn it on for a couple of hours whilst I was in the house doing some work (I wasn't living there yet).
The next day I come and the water was luke warm at best and needed to reheat the hot water cylinder again.
This was between Jan to march time this year when it was super cold.
Completely typical of the old tanks. Don't disagree. That was pretty much what you faced and hence why you would heat water twice a day.
Then wrapping with a thin piece of glass fibre in a plastic wrapper helped a bit. But probably not as much as people thought.
Modern tanks are nothing like that. They are in effect coated in the same stuff as PIR from the factory, with the access holes etc cut out.
They do not even feel warm to the touch when the inside water is 60+C