Water heater

matelodave

It will only change over at midnight (or 1am in the summer and switch back at 7am (or 8am in the summer) if you've got an E7 (off peak tariff).
You need to read both registers, if only one is incrementing then you will be on a single rate tariff - what does your bill say or wha did you sign up for, Ideally if all you've got is electric radiators/panel heater then the last thing you'll want is an E7 tariff because you'll be using them during peak rate times.. Take daily readings of both registers one when you get up and one before you go to bed for a week or so to find out whats using energy and when
You really do need to understand what you've got so you can use it properly otherwise you'll be crucified with high bills, likewise you need to ensure that you are on the best tariff for your circumstances