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Immersion Heater

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vulcan42 | 10:51 Sat 11th Apr 2020 | DIY
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I have a 36"X 18" (92 X 46) hot water cylinder and the immersion heater has stopped working. Can anybody tell me the heater size (length) of the one I need to fit that cylinder please? I know I can remove and measure but with so many shops closed I want the right size heater to hand before I start.

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Yes a 27" element is needed.
15:30 Sat 11th Apr 2020
I think some go in at an angle at the top of the tank and others go near the bottom, horizontally. Which is it? (I'm no expert at these things, btw!)
You can put whatever length you want into a cylinder that tall. The length simply determines the amount of hot water that you get so, if all you want is water at the kitchen taps a short one will do; if you all shower one after the other then a long one will be better.
I assume you have checked fuses before you commit to a new heater. If you've never changed one before I'd recommend buying the special spanner and be very careful - it's easy to wreck the cylinder trying to unscrew a heater which has been in place for many years.
‘ The length simply determines the amount of hot water that you get‘

That’s not correct. A shorter element just means the tank will take longer to fully heat.
Your first thing to check is the thermostat, you may not need a new heater.
Easiest way to check the thermostat, if you have no test equipment, is to look at the wiring. Your live feed goes into the stat then leaves the stat and goes to the live connection of the heater. Simply disconnect the stat and put your live feed directly on the heater. If heater now works then your problem lies with the stat. Observe all the safety measures for electrical work.
Zacs - they make dual length heaters; the long element is used to heat the whole tank, the short element heats only the top part.
The short element can also be fitted horizontally near the bottom to heat the whole tank.
BTW, if the heater works without the stat, don't leave it wired that way or the water will overheat. Buy a new stat replacement.
Atheiost , I took it for granted that would be done but better mentioned.
This is a useful guide to what sort of heater to fit:

http://www.free-instruction-manuals.com/pdf/pa_1936613.pdf

If you have to remove a horizontally fitted heater then just drain enough water to be just below the heater , the remaining water gives some strength and stability to the tank.
Just take out the stem thermostat..no need to drain anything..this will tell you the length.you can then do a continuity test on the stat.It may have a re-set button.If you replace the stat, get one with a dual cut out.This is a requirement especially if you have a plastic header tank in the loft above a bedroom.
Immersion heaters create thermals in the tank. The hot water doesn’t just stay at the top.
Hot water rises; a long heater will produce temperature rise near the bottom of the cylinder and result in more hot water than a short one. A short one will heat the upper layers of water and conductivity will take some of the heat towards the bottom, but very slowly.
Exactly, so a short element will be expensive. I think Vulcan should be aware of that if he’s wanting a full tank.
ZM a short element would probably be cheaper as it would produce less hot water. But of course that might not be what the OP wants.
Thank-you Atheist for explaining things more fully than I did.
The element may be cheaper but Vulcan needs to know that he’d be paying much more to heat a full tank in the long run.
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Many thanks to all your answers, interesting as well as informative. I have by passed the thermostat and heater not working. The thermostat measures 18 " overall so I assume a 27" heater would be OK, ?
If it's a 36" cylinder a 27" heater should fit. Have a look at the link I posted at 12:24 as they have recommendations as to which to choose depending on your water hardness etc.
Screwfix are currently doing Click and Collect only and say they are queueing outside the store for safety.

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