It might be worth knowing that Bathstore brassware is Crosswater rebranded. You should be able to ID and get instruction for the appropriate Crosswater model.
This sound like a dual fuel towel rail, runs on the CH in the winter and electric in the summer (as the CH isn't running). Plumbbob is bang on, the only other thing you normally have to do is shut the one of the rad valves other wise you will try to heat your entire heating system with this small el...