How to prepare to change an immersion
You will need a screwdriver and a length of hose long enough to reach into the garden or down to a grid in the road outside.
Step 1 - Turn off water at stopcock
Make sure your water is turned off - you'll be partially draining your tank later and you don't want it to keep refilling!
Step 2 - Turn off electricity at consumer unit
You also need to turn off your electricity at the fuse box as the immersion heater element is connected to the mains.
Step 3 - Partially drain hot water cylinder
You'll need to partially drain your hot water cylinder before you begin, but before you start you need to take precautions to stop your hot water taps from becoming air locked, or your tank collapsing.
An air lock is the term used to describe a situation where large bubbles of air block your hot water pipe at the tap, creating pressure that stops the hot water from getting through.
Fortunately, it's easy to avoid falling into this trap - all you need to do is fully turn on all of the hot water taps in your house. As an added bonus, this will help your hot water cylinder drain a little faster.
Turning on your hot water taps will not drain the tank. This is because the hot water is taken from the top of the tank, not the bottom. The cold water entering the tank pushes the hot water out.
Leave your hot water taps fully open - even if no water comes from them. It's now time to drain the cylinder. You'll need to attach a hose to the drain valve (also referred to as a drain cock). You'll find this at the bottom of your hot water cylinder attached to the cold water inlet.
These valves can be a bit leaky, especially if they're old, so it's worth putting a towel or two down just in case.
Make sure that the end of the hose is outside, either in the garden or near a drain in the road. Open up the drain valve using a radiator key or adjustable spanner. Your cylinder will now begin to empty.
There's not much you can do now other than wait for the water to run out of the cylinder.
You only need to drain the tank down as far as the immersion heater you are working on.
It's not possible to see into the cylinder to judge how much water has run out, so leave it for around 5-10 minutes before you close the drainage valve up again.
Why shouldn't you fully drain your hot water cylinder?
The walls of the hot water cylinder are quite thin and vulnerable to damage from the application of force.
When you start to loosen your immersion heater element, there is a risk that your cylinder might distort. A cylinder is referred to as being 'distorted' when its wall buckles or creases. Once the copper walls of your hot water cylinder are distorted, they are weakened and could rupture without warning.
Leaving water in the cylinder helps to reinforce the copper walls by applying pressure against them. The weight of the water also helps to reduce the risk of turning the cylinder itself and distorting the pipes that connect to it.
Step 4 - Clear obstructions to immersion heater element
If your tank is insulated then you will need to use a cranked spanner, a box spanner or a box ring spanner.
You may still need to clear some of the foam insulation away from the immersion heater element. You can do this with a stanley knife and a screwdriver - use the knife to cut around the section of foam that you want to remove and then carefully prize it out with the screwdriver.
If your immersion heater element is recessed then you will need to remove the safety panel that covers it so that you can access it with the spanner.