replacing immersion heater

I need to replace the immersion heater in a traditional hot-water cylinder (with a cister and a coil heated by the boiler). The existing model is labelled "HEATRAE GOLD DOT / 2.3--3 kW / 210--240 V AC ONLY / LENGTH 27" FIXING V". (The element was installed at least 17 years ago.)
I see from googling that the Heatrae Gold Dot product in 27" size still exists. Can I buy one, safe in the knowledge that the thread will be the same? (In other words, I won't get a nasty surprise when I've drained the hot water & unscrewed the old element, & am about to try putting the one in. I'd really prefer not to have to leave everything hanging open while I cart the old element to a shop for comparison.)
Also, are there any tricks for getting the water level in the cylinder below the fitting for the element? Or do I just shut off the water to the cistern, run as much water out of the hot system as I can, and then mop up what runs out when I unscrew the old element?
Thanks, Adam
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Adam Funk wrote:

Most HW cylinders will have a drain cock tucked away at the bottom somewhere but not always. It's a good idea to have the cylinder *full* of water before attempting to unscrew the old element though, it may require a lot of force and having the cylinder full of water makes it more rigid and less prone to damage.
If you can't find a draincock I think you just have to shut off the supply, drain what you can and have some towels handy. You could disconect the pipework at the top and syphon water out with a hosepipe but I suspect that is overkill (assumming the element is inserted down from the shoulder at the top of the cylinder).
Tim
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On 2012-02-08, Tim Downie wrote:

Thanks. I agree about having the cylinder mostly full to keep it heavy and stable.
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On 2012-02-09, tony sayer wrote:

Thanks; I'll be careful...
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Until you get it turning, I would suggest tapping the wrench (not too hard, of course) rather than prolonged pulls or pushes (and grunts), and also a bit of 'forwards and back'.
--
Ian

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On 2012-02-21, Ian Jackson wrote:

Thanks.
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On 08/02/2012 15:08, Adam Funk wrote:

AFAIK the thread hasn't changed in a very long time. The problem with draining is that the DHW supply normally comes from the top with the cold feed to the bottom. Not usually much spillage with a top entry element; you *do* have a wet and dry vacuum cleaner, don't you? If the element is side entry at the bottom, you need to hope your plumber fitted a drain cock on the cold feed.
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Not done one of those in years
Hated the job with a passion
When I did do them getting the old ones to unscrew without trashing the tank was the real challenge
As to getting water out after shutting the water off this can only be done by a drain on the cold water bottom feed which was usually on the side of the tank rather that at the front. And often the airing cupboard was built around it afterwards
Hot water storage tanks force the hot water out of top when a tap is opened due to the header tank being connected to the bottom
Best of luck
Regards
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water off at mains, drain thro hot taps till they stop. Disconnect wiring (safely), hammer and chisel and knock the edge of the nut of the heater till it moves then unscrew with immersion spanner. Refitting with a small amount of sealant on the fibre washer and nip up with spanner. Reconnect refill and check for leaks.
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On 08/02/2012 16:37, TMC wrote:

Yes, I got mine out once, but I then had to change the tank anyway, and it was impossible to get the element out a 2nd time.
--
Michael Chare

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On 2012-02-08, Newshound wrote:

No, but I have lots of old towels and rags. ;-) I checked and the element's fitting is really close to the top of the cylinder, so even if I can't find a drain cock, I don't think a lot will run out.

I haven't found the drain cock yet, but the airing cupboard is rather tight and I haven't rummaged thoroughly.
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On 09/02/2012 12:15, Adam Funk wrote:

Seriously, a wet and dry vac is one of the most useful plumbing tools you can get. The plastic Wickes / Earlex cheapie is fine.
Apart from your cylinder job, you can use them to empty gullies, catch the water when draining a washing machine, dry up after defrosting a freezer, empty the pan of a blocked loo, empty blocked sinks before opening the trap, catch the muck when you need to drain a radiator, to name but a few.
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I have a George would not be without it
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On 2012-02-08, harry wrote:

Thanks very much for the advice. I'll be careful!
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