How to replace an immersion
Step 1 - Attach fabric seal
Your new immersion heater element will have a separate fibre washer, also called a fabric seal or fabric gasket. Slide it down around the element coil and make sure it's snug against the base of the inside of the heating element.
If the washer is damaged, do not use it, replace with a new one. Never re-use fibre washers.
The washer should be enough to make sure that there are no leaks, but, although not reccomended, it is possible to smear it with jointing compound.
Wrap 2 or 3 turns of PTFE tape tightly around the thread, anti-clockwise if the element is facing down. This will help prevent the threads from binding and allow a tighter seal. Keep the PTFE tape clear of the fibre washer and sealing face.
Step 2 - Clean copper boss
Clean away any limescale on the top of the copper boss using an abrasive such as a file or scouring pad.
If the top of the boss is not flat then this could cause leaks when you install your new immersion heater element.
Step 3 - Insert new immersion heater element
Carefully slide the element coil into the cylinder and screw the element base clockwise into the copper boss.
If you encounter any unexpected difficulty when tightening the heater element, you may have crossed the threads. Unscrew the element until you hear a click, and then try tightening it again.
Step 4 - Tighten immersion heater element
Using your immersion heater spanner, screw the new element in nice and tightly. This will ensure that it makes a good seal against the hot water cylinder.
Step 5 - Check for leaks
Make sure your drainage valve is closed and turn the water back on at the stopcock. Your trusty hot water taps should still be on at this stage and once again they're going to let you know what's going on inside your tank.
Once water starts to come out of them again in a steady stream, your tank is filled. You can now check for leaks. If water is escaping your tank, your immersion heater needs tightening some more so crack out your immersion heater spanner once again!
Step 6 - Reconnect power
Once someone qualified has reconnected the wiring to the new immersion heater element you can switch the power back on at the fuse box.
Now that your brand new immersion heater is installed, it's only a matter of time until you can enjoy a relaxing, hot bath!
If you had to make any holes in your tank's insulation to access your immersion heater or to apply heat to it, you can now make repairs using expanding foam.
Just follow the instructions on the can! Remember, the clue is in the name. Expanding foam expands, so use it sparingly to start. The foam doesn't always expand immediately, and will keep on expanding for a little while.