Electric water heater off or on ?

[RayB]

Is it cheaper to leave my electric water heater on all the time? Its a well insulated ballon very common over here in France. I had put it on a timer to heat up at night on cheap rate electricity but someone said its better to leave it on.
Ray B

 

[Diyisfun]

If its cheaper at night & by being on all night is all you need, then how can it be cheaper to leave it on.
Anyway even if it wasnt cheaper, it is not the most economical way to heat the water by leaving it on, UNLESS it is in constant demand.

 

[RayB]

We use the water by day, showers washing up etc. I let it heat up the tank overnight (250 Lts I think) and nomaly lasts all day. Now summers here we get a lot of visitors so it would need a boost during the day. BUT! I was told that if you leave it on all the time it just heats up what you used and cuts in to top up the temp when needed, rather than heat up the whole tank. I can see the logic but being thick I'd thought I'd ask the experts! Can any one shed light on this theory?
Ray B