It's been a long time since I had anything to do with storage heaters, but, a quick outline. The heating of the bricks within the heater is done over night on a cheaper tarrif, the output or heating was controlled via a 'flap' of sorts, the more open the flap was, the more heat came out ( a very crude explanation ) sorry if I'm stating the obvius. Can you give us the make and model of the heaters, might be able to give a bit better guide that way