There is a chance that you will have to replace the immersion heater around twice during its life-cycle. Whilst fitting animation is fine you might wish to ring an electrician to get it wired up after. A Neasden Plumber can change an immersion.

Tools and materials:
Electrical tester.
Small adjustable spanner.
Electrician’s screwdriver.
Sponge/towels.
Immersion spanner.
Hammer.
Abrasive strip.
Jointing compound (drinking water suitable).

Method: Use an electrical tester to check that the immersion heater is actually getting power. If it isn’t call out an electrician.

Assuming it is defective, isolate the electrical supply to the heater.

1). Usually the immersion heater is set in the cylinder on the top. Use an adjustable spanner to remove the securing bolt from the immersion heater cover, double check that the electricity is off, then remove the three wires (live, neutral and earth) from the old immersion heater. Insulate the bare ends and tuck the cables safely out of the way.
2). Using an immersion spanner or a large pair of pliers unscrew the old immersion heater anticlockwise.
3). Once you’ve broken the seal, the immersion heater can be wound out. There may be a slight dribble of water. Neasden Plumbers will do a professional job.
4). Clean the threaded hole for the immersion heater. Scrape away any foam and place the fibre washer over the new immersion heater. This will provide a waterproof seal. However, it’s not unknown for leaks to occur so you may want to apply a small amount of jointing compound to the thread of the immersion heater, ensuring that it is suitable for potable water.
5). Tighten the new immersion into place. Re-open the valve for the water supply. Leave all the hot water taps open and let water start to emerge before turning them off. Keep an eye out for any leakage throughout this process. You have a leak in the emotion another time with your immersion spanner. If unsuccessful you may have to start again and re-sealing.
6). As long as evidence dry, reconnect the live, neutral and Earth, of course if unsure seek the services of an electrician.