Have you checked the setting on your storage heater input?

Your night storage heater input control determines how much heat your heater stores overnight. How high you set the input, depends on how chilly you think it the temperature will be the next day. If you think it will be cold, turn the setting up, if not turn it down. The higher the setting, the more electricity the heater will use, and it will also cost more to run. Changes made to your input setting won’t take place until the following day.
 

You can find out more about night storage heaters on our Electric heating webpage.