Immersion Heater Not Heating?

Since my gas boiler went wrong (waiting for warmfront to replace), I have been making do with my electric immersion heater. Usually it supplies enough hot water for at least a bath and has been a life saver while i wait for my gas boiler to be replaced.

However, suddenly it isn't working anymore. It has a dedicated switched power supply and this switch has a light to show that it is on. The light is still on but the tanks and pipe are cold.

This is my only way of heating water now, short of boiling lots of kettles and any help would be appreciated!