The IH should be fed via a 20A double pole switch which you can turn off. It should be visible to you whilst working on the heater so that you can be certain noone has turned it on again whilst your back was turned.
If you can't see it go to the CU, flip the circuit OFF and put a DO NOT TURN ON notice on it!!
ALWAYS "test for dead" - even if you think you've done what you need to do. Take note of the way the cable is connected to the heater before removing the wires.
Get yourself a proper Imersion Heater spanner BTW - box type is best.
[quote="danny s"]what action should be completed before i start working on my replacement of an electric immersion heater :cry: do i get a electrian to look at it first or what?[/quote]
don't forget to part empty the tank.