Storage Heater with one dial

Avoiding any comments on the installation

I don't know that particular heater - it looks like it may have a convector heater on the front, and a storage heater at the back. If it gives instant heat from the front grille maybe one of those switches controls that directly. Try switches one at a time and see if any heat comes from the front. Hopefully someone here will know that model?

if not:
Turn both switches on the wall on (unless you have established that one is specifically for the convector, in which case leave that off).
Maybe turn the knob on the heater clockwise between half way and full.
If you are still up after midnight, check to see if lights on the heater (the two black squares on the left which I don't think are switches) are lit!!
Wait until next morning to see if the heater gets hot.

There is a chance that the heater may require attention, or that the cheap-rate electricity feed to it (to store the heat) is no longer functioning.