immersion heater

9 May 2008
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United Kingdom
Hi, just recently moved to a house that has Oil fired CH & DHW sytem (fully pumped). I wish to fit an immersion heater for hot water only during the summer months as I did at my previous properties.

Does anyone have any suggestions on removing the cap on the top of the tank as it wont budge? at present the tank doesn't have an immersion heater. I've read other posts about how fragile the copper cylinders are and don't want to do any damage. I have a decent fitting socket and large extension bar.

I've been able to partially drain the tank and isolate the cold water feed to the system.

All the electrics are in place and have been checked by an electrician. For the sake of an immersion heater and new flex we'd be there. It just seems the previous occupants were happy with this arrangement.

Any advice suggestions I'd be gateful.
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For a start only loosen the plug to get it to start turning with the cylinder FULL !!!

Be prepared to damage and have to change the cylinder.

I would say the maximum torque you could safely apply is a strong man with a 300 mm long bar.

A 600 bar could damage the cylinder but of course would have more chance of loosening it.

A 900 mm bar would have a good chance of loosening or damaging the cylinder.

These are with a strong man, not an office worker!

It might help to warm the socket with a gas torch.

i know what you mean, the previous owner blanked off the immersion heater boss with a cap. and over time it has got stiff and stuck! using heat may be a good idea, or some other type of lubricant also might help. as said before though be careful as you don't want to have to buy a new cylinder at 160+ pounds!! :)
It's the same problem as removing an old immersion heater. There have been quite a few suggestions on here, including:-

Heating up the plug,
Starting off by tightening it up a fraction to break the seal,
Drilling then cutting across the plug with a jig saw / pad saw, and collapsing it inwards,
Brute force

Before adopting the brute force approach, check the price and availability of a replacement cylinder. Sod's law states that you will only break it if a replacement isnt available
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Thanks to all of you for the rapid response. I take on board all your comments and I'll have a think before I attack it again.
As opposed to putting a lot of pressure onto it give bar a couple of sharp hits with a hammer to shock it loose
Had a day off today and attacked it again. After following all your advise I decided to drill the cap with a decent 8mm drill across the middle of the cap. With a hacksaw blade cut the threaded section of the cap at both edges, then cut down as far as the washer. Take care when cutting down as I marked the sealing face, I cleaned this with some emery cloth. Quick tap and the two halves came out. Now have immersion installed and heating the water. Thanks for all your input.

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