My Dimplex XLN storage heater is not heating up?

I turned the heater off 3 years ago when I moved into my flat as it was too expensive to run. I am now selling and was checking that it still works however no heat is coming from it. I did have my electricity meter changed two years ago to one which has a single rate rather than the tariff which is cheaper at night. Would this make a difference or could it be that I may have to reset it (I do not know how to do this)?