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How do you prepare to change an immersion heater element?

How to prepare to change an immersion
heater element

Shop for Immersion Heater Spanners

Image of the tools needed to prepare your immersion heater element for removal 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.
Image of a stopcock

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!

Image of someone turning off the electricity at the consumer unit

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.

Image showing an air locked tap that is not allowing water to flow out of it properly

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.

Image to illustrate an air locked hot water pipe 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.
Image to show running the hot water tap to prevent an airlock 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.

Image showing the location of a drain valve in an airing cupboard 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.
Image showing an old valve that has sprung a couple of leaks 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.
Image to show leading the hose attached to the drainage valve out into the garden 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.
Suggested activity while waiting for the hot water cylinder to drain 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.

What to do while your hot water cylinder is draining

Why shouldn’t you fully drain your hot water cylinder?

Image showing a split hot water cylinder The walls of the hot water cylinder are quite thin and vulnerable to damage from the application of force.
Image to show what a distorted hot water cylinder looks like 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.
Image for reinforcing a copper cylinder 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.
Image of a box immersion heater spanner

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.

Image to illustrate removing polyurethane foam to make enough room for an immersion heater spanner head to be fitted around the immersion heater element 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.
Wonkee Donkee reassures the DIYer that you can replace any polyurethane foam that has to be removed
Image to show cylinder with recessed immersion heater element 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.

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