Gas Boiler DHW demand

[Gas Boiler DHW]

Why is there a choice in choosing time periods for DHW on gas boilers?….Why not having DHW ‘on’ 24hours/day.
Isn’t the boiler switched on only on DHW demand ?…hence no need for setting time intervals for DHW.

 

[Deleted member 120897]

There is I believe it’s called constant.

I think the timed periods is because (certainly newer well insulated cylinders) will last so long before needing to be reheated. I have mine on for 3 timed periods per day and this will last throughout the day. If it was on constant then it would be heating unnecessarily all day wasting energy.