Hot water cylinder cold at bottom

[TURKEYNECK]

Hello my cylinder is heated overnight by immersion element for about 4 hours plenty of time to reach hot and heat all the water. But before its used I feel the top of the cyl and its hot but the lower half is cold.
Id expect the element to heat all the water eventually, thus we get two approx 4minute showers.

Its an older tank, not foam covered.

I wonder if the previous owners (weve moved in 12mth ago) had a short element installed as an energy saver as there were just two of them?
Is there a leak so cold water is fed in slowly continuously?

anything else?
many thanks
Turk.

 

[twgas]

if the immersion is fitted at the top of the cylinder it will only heat down the length of it, 11, 18 and 27 inches are the usual lengths.
You might have top and bottom elements, the bottom one should heat the whole tank, apart from the lowest few inches, the top one would only heat the top 10(or so)inches.

 

[TURKEYNECK]

thanks Mick, yes just one top mounted element.
ok so the short element is the economical choice .. by that I mean the water should slowly cool during the day needing a small top for an evening shower .. as opposed to a longer element heating most of the water so hot water last longer ..
Im going to re-insulate the cyl as it was boxed in and insulated with this loose 'stuff' .. horrible dusty stuff (masked myself up). Ive got new a Wickes jacket (£10 reduced to £3) .. are they any good .. I guess new foam tank and fittinf will coswt best part of a grand?
Turk

 

[JohnD]

if you can still get the red jackets at that subsidised price fit two of them, one on top of the other, and overlapping the joints between segments. Also fit foam pipe lagging on all the hot pipes. The electricity saved will repay the cost in a matter of weeks. You will also find that unused hot water stays usable for 24 hours after heating.

You can get a switchable dual-element immersion heater that fits into the same boss at the top of the cylinder. They have a long element and a short element (they are both the same power, so the short one heats a small amount of water faster than the long one heats a large amount) but if the cylinder and existing element are old, it can be difficult to unscrew the old one, it may be seized in place. This is one of the times when an experienced old plumber may be able to do the job without damaging the cylinder, better than you can. That would IMO be worth doing, it will be a lot cheaper than changing to a modern cylinder. If you doi change cylinders, IMO go for as big a cylinder as will fit, with an upper and a lower element. Do you not have a gas boiler? It would be cheaper than using electricity. Do you have night storage electric heaters?

 

[TURKEYNECK]

Hi John, I have no night storage heaters, I have economy seven but thats being changed to single rate (at retro billed at single rate 12mths) due to npower mixup.
I like the idea of dual element, there are just two of us but frequency have family staying like this last weekend so a full (ish) hot tank would have been cushti.
I did install an economy 7 timer and its the hosrstman manual jobbie with boost dial .... I wonder if this would serve the dual element?

 

[JohnD]

do you have a gas boiler?

 

[TURKEYNECK]

lpg .. bulk purchase at about 50p/litre ..

good point .... will the gas boiler heat up the whole tank?

 

[JohnD]

all but a few inches at the bottom... provided that it is an indirect cylinder with a coill in it, and is plumbed to the boiler.

Most gas boilers have at least five times the power of an immersion heater so can heat the cylinder faster as well as cheaper. It needs a cylinder stat and insulation on all the hot pipes.

 

[TURKEYNECK]

ok its got a stat, its old so for the small cost will replace it .. but I assume that for the boiler heating control .. the immersion will have its own stat I assume ..

time to check boiler out ..