When does cold water enter my hot water tank?

[rich761]

I have an electric, Amptec central heating system:
There are heating tubes, in the airing cupboard, though which water is pumped. As the water cycles through these tubes, and back to the hot water tank (in the attic) it gradually heats up.

What I'm left with, after the central heating has been running for an hour or two each morning, is a tank in the attic which is full of hot water. The heating tubes are not used outside of the central heating timer programme.

I would like to know when new, mains water enters the hot water tank outside of the central heating timer programme (if it enters the tank at all, during this time).

If I used the shower, then is cold mains water taken in to replace the water used by the shower? Or does this process wait until the central heating next runs?


Many thanks in advance,
Rich

 

[Dan Robinson]

You've totally lost me.

 

[calorific]

He's asking if cold water blends into the tank with the hot when a tap is opened, or if this does not take place and the tank is not topped up with cold until the heating elements are turned on at the preset times.

If the latter, then the tank will never become luke warm (other than heat loss) and supply hot water until it empties, or the timer turns the heater back on.

I think I might have made it even less clear

 

[rich761]

Basically, when I use the shower, is cold water fed into the hot water tank, to top it up immediately, or does no new water enter the tank until I turn the central heating system on?

I hope that makes more sense

 

[rich761]

calorific, that is *exactly* what I'm asking. Thanks for your help.

 

[Dan Robinson]

I need a drink


OP.

If I get you...

When you draw hot water off, cold water enters the bottom of the cylinder via the cold water tank in the loft, that is fed from the incoming mains water pipe.

It is not heated until the timer and thermostat both agree to do so.


Perhaps a few pictures of your set-up would help?

 

[calorific]

I need a drink

In fairness, I've already had a few and the op makes perfect sense to me

 

[Dan Robinson]

I have two more estimates to write... then balls to it... Nearly finished watching Return of The Jedi, the dude is asleep and i have an early start in the morning; and a long long day. A very stiff G&T is on the way.

 

[rich761]

This is the closest I can find online:
http://www.partsarena.co.uk/baxi/System/DATA/Dx/DS1/installation/3999/I51-3999/I51-3999-F006.gif

If it helps, there's one expansion tank (it has a pressure gauge on it and it is connected to the main tank, so I'm relatively sure it's an expansion tank). This and the main, larger tank (which stores the hot water) are the only tanks in the house.

 

[calorific]

If the water is not replenished instantly, then the hot water would come out somewhat slowly due to it being "held" in the tank by a vacuum effect, and even if there was some kind of automatic air vent then at best it would come through the shower at low pressure (gravity fed). Assuming that you haven't got a cold water tank up there and that the cold supply to the shower is mains pressure, it seems logical that the tank is replenished instantly in order that mains pressure to the taps is upheld.

I too will be interested to hear from the pros if I'm talking blox

 

[rich761]

Thanks for your reply, calorific. The hot water pressure is actually much lower than the cold water pressure, so maybe the water isn't topped up instantly. Perhaps it is 'gravity fed', as you said.

 

[TicklyT]

The answer is 'Stratification'.

The amount of water in the hot cylinder is constant. Gravity causes cold water from the cold storage cistern to run into the bottom of the cylinder as hot water drawn off from the top. If it didn't, the cylinder would have to collapse like a punctured balloon every time you turned a tap on (under some extreme fault conditions they actually do )

As hot water is less dense than cold, it migrates towards the top of the cylinder, and the cold water stays at the bottom. The two layers don't mix to any great extent so the hot water stays hot until almost the whole cylinder full has been used.

When the top of the cold water layer inside the cylinder passes the level of the thermostat strapped to the outside of the cylinder the thermostat cools down and closes, calling for the boiler to re-heat the cylinder.

 

[rich761]

Thanks very much for your detailed answer, TicklyT. Today I learnt about 'stratification'

Your post told me everything I wanted to know.

The only small point I'd like to make is that there is no cold water storage cistern; there simply are no other water tanks in the house/attic/etc.. I don't believe that makes a difference to how helpful your post was, however, since I very much expect the process is the same, regardless of where the cold water - entering the hot water tank - comes from.


Thanks again.

 

[Charnwood]

The short, concise, laymans answer is 'as soon as you turn on a hot tap'.