sounds like to me a loose connection in the box.
My adivce would be get a electrician in.... unless you feel confident to a bit of diy. if so you will need to isolate the supply to that heater. go to where the main consumer board is that controls the circuits for the Block storage heaters (usally a seperate consumer/fuse board, that only controls these heaters ) & turn the main switch to OFF this will switch all the heaters off in your residence (((( If you ar not sure where this isolation switch is DONOT try to fix this problem. ))) if you do know then Make sure you have the supply off to the Heaters, then remove switch plate from the box, then check the Switch & Wires for any burnning if so you'l need to change or cut off the affected wires & then reconnect into where tthe wires came from. Make sure you DONOT mix up wires where they came from or your have a bigger problem when you turn back on the power again. As i have said DONOT do anything unless you are able to take this task on...
colin
January 2010