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How do you replace an immersion heater element?

How to replace an immersion
heater element

Shop for Immersion Heater Spanners

Image to show where on the immersion heater element the fabric seal has to be applied

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.

Image to show a tradesmen wrapping the screw thread on an immersion heater element base with PTFE tape 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.

Wonkee Donkee says that even though plumbers can use PTFE tape and jointing compound on an immersion heater element, they are not needed and can make the heater element get stuck in the copper boss in future
Image of a DIYer removing limescale from the top of a copper boss on a hot water cylinder using a file

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.

Image of a DIYer inserting a heating element into a hot water cylinder

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.

Image of DIYer tightening an immersion heater element using the immersion heater spanner

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.

Image of a stopcock

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!

Image to illustrate turning the power back on

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.

Image of a cat enjoying a relaxing hot bath because his immersion heater has just been replaced and is working perfectly! Now that your brand new immersion heater is installed, it’s only a matter of time until you can enjoy a relaxing, hot bath!
Image of expanding foam, to be used to reinsulate the hot water cylinder 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.

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