Why is my storage water heater not working at off peak times?

Looking at your image, you have both the Normal Supply and Off peak supply switches in the “On” position. What kind of meter do you have for your electricity? If you are not sure, it would be helpful if you supplied a picture of the meter so that its associated wiring can be seen. There are a number of people here who are experts with heating and hot water in all electric properties.In the meantime, I would turn both switches off. I believe that the Normal Supply switch is only for use if you need to top up your hot water during the day for some reason when you then use the Boost buttons. I have found a link to this controller and there is also a link on the same page for a user manual. I am not sure that this will fix your problem. https://www.securemeters.com/uk/product/electric-water-heating-controls/bx2000-hot-water-boost-control/

I have a pre payment meter and I have also has to turn both switches off as it was charging me 62p per hour just now. I would have to look for a user manual. Thanks for the link!