It's probably the same timer turns on the storage heating circuit as turns on the night time electricity meter. So I think you'll be charged night time rates for the storage heating despite it on during the day. The timer just has the wrong idea of when night is. (I think this is how it works, it's a while since I lived with the bane of storage heating.)
The ESB would not be happy if you're getting night time rates during the day, so the safe option is to tell them you think it's wrong instead of them telling you.
When it's fixed your bill could rise if you're currently inadvertently making use of night time rates during the day (for cooking, TV, lighting as well as storage heating).