"Changing Immersion Heater" Hot water tank

[johnnyjb]

Hi this is my first post

When changing element of hot water immersion tank how do i drain the tank,does the element generally screw off easily and do i have to seal the threads up again with some adhesive tape ,the kind plumbers use

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Moderator's note:

I will move this to "Plumbing" as it is replacement of an existing.
I have also added to the Title (in quotes).

Mod Rupert
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[kevnurse]

This is predominantly a plumbing question.
Are you sure the problem is the heater element? There is a thermostat that is replaceable (disconnect it from the wires and pull it straight out) without removing the element. It is strongly recommended that you make sure the stat is not at fault.

The tank will have a cold fill pipe at the bottom, which should have a valve nearby to stop the tank from replacing the water as it is drawn off from the top. Having closed that valve, you then need to open all the hot water taps in the house and wait until they all stop pouring your money down the drain. The hot water system, incl the tank will then be empty. Don't think that you can draw off water at the top of the tank only. The system acts like a big U tube and you will find it difficult to find the level in the tank. If you have no isolation valve on the cold feed, you will have to isolate the pipe where it comes out from the bottom of the cold water cistern.

The immersion heater element requires a special spanner which looks like a large one ended ring spanner. Unless you want to risk buying another tank, buying the spanner from a plumber's merchant is the insurance premium you have to pay. Its a standard size, but feel free to measure across the flats if you want to know the size.

When fitting your new heater, you will also need some PTFE tape, also available at the plumber's merchants, to wrap around the threads.

 

[JohnD]

It can help to loosen the big nut a fraction while the cylinder is still full of water - the copper cylinders are paper-thin and will crease or tear easily if you heave at the big spanner (you might be able to hire one). Being full of water helps it to keep its shape a bit.

I think the box-spanners are better than the flat ones.

 

[kevnurse]

I agree on all counts.

 

[Softus]

It is strongly recommended that you make sure the stat is not at fault.

Good advice.

The tank will have a cold fill pipe at the bottom, which should have a valve nearby to stop the tank from replacing the water as it is drawn off from the top. Having closed that valve, you then need to open all the hot water taps in the house and wait until they all stop pouring your money down the drain. The hot water system, incl the tank will then be empty.

Er, it will still be full. You can't empty a cylinder from a hot tap.

being full is actually preferable because it's helpful for the tank not to move around when loosening the IH.

If the element is top-mounted, then apart from stopping water from entering the cylinder (and also emptying the vent pipe) you don't need to drain the cylinder - a large towel will be enough to catch the small amount of water that emerges from the IH hole. If you have a wet-vac then you'll find it useful here.

If the IH is side-mounted, then you have some draining down to do. You can risk opening the drain cock at the bottom (and then find you can't shut if off again without completely draining and replacing the washer), or you can siphon water off by removing the top connection and sticking a hose into the hole.

 

[kevnurse]

Yes, I did think about my suggestion about the taps after I sent the message. I confused myself with my own house when I had to drain the cold water cistern (leaking outlet connector). With all the cold water taps coming off the rising main the only way to drain the cistern was to use the hot water taps. Of course, the water in the hot water tank will never drop below the point at which the hot water is drawn off (ie the top).