On 24/11/2019 10:32, Lee Nowell wrote:
Hi All,
Well I think that's what it is. It looks similar one of these
https://www.unventedcomponentseurope...-95605886.html
In my situation the large black bit is positioned to the left and
the other ports are Top - cold water feed to house Bottom - mains
water feed from outside Right - connected to top of h/w cylinder (it
is a mega flo type thing for mains pressure hot water)
Not sure the connections as described make sense - although that depends
a bit on what you mean by the connection to the top of the cylinder.
The cold water control valve normally provides a supply of mains cold
water to the cylinder (through a strainer to catch particulates), at a
reduced pressure. Normally it facilitates a connection to the main DHW
expansion vessel, and usually provide a pressure balanced cold output
for use in the house in situations where having equal hot and cold
pressures is particularly desirable - e.g. showers.
See:
http://wiki.diyfaq.org.uk/index.php/...ted_cylinde r
The leak is coming from the big black bit but not at the end
somewhere between the brass bit and the end.
Dismantling, cleaning, and (possibly) descaling will often help
I have done some googling and there seems to be a mix of views 1.
This is normal and that's what happens when the pressure is high.
Seems odd to me and mine continually drips. Also not sure what
pressure is too high - boiler circuit is set at 1.5 bar and inbound
Nothing to do with boiler circuit pressure - that's not connected to the
incoming mains water directly.
pressure is not great 2. It is because the expansion vessels have run
out of air. I appear to have 2. One in the inbound supply side and
one on the circuit coming out of the boilers. Some people seem to say
to just check them and if low too them up (not sure to what) with a
tyre inflator (presume the little compressor thing I use to pump
tyres up).
If you turn off the cold water feed to the cylinder and go draw some hot
water from a tap, you would expect it to keep providing water at a
reducing pressure for a short while - basically the stored compressed
air in the expansion vessel will push some more water out of the
cylinder even without the incoming mains pressure. If you don't see
this, then that is a good indication that the vessel is de-pressurised
(you would also expect water ejected to the tundish each time the
cylinder heats up).
Others say this is very dangerous.
They would be the ones who don't understand unvented hot water
cylinders, and prefer the "there be dragons here" policy over self
education :-)
If you turn off the cold main to the cylinder, release any stored
pressure by opening a hot tap, you can then measure the pressure in the
vessel. Then re-pressurise with a pump to the manufacturers recommended
pressure.
Also TBH not sure what
the purpose of either is and therefore which one is likely to be it.
If safe, I could do both of course.
It allows the water in the cylinder to expand when its heated. Without
it, and an otherwise closed system the pressure rise would be very high
(and then typically open a safety release valve to discharge into the
tundish)
3. The valve is faulty and it
needs to be changed by a qualified person as could be dangerous.
It may be faulty, or may just need cleaning. How much qualification do
you need to turn a spanner?
There are safety concerns with unvented cylinders, but these are
addressed by the overall system design and that of the controls. Doing a
like for like swap with the appropriate part carries no risk beyond that
associated with any plumbing job IMHO.
I have done a lot of plumbing including designing and fitting the
whole plumbing (obviously no gas work!) in our last place and adding
to the current one so am pretty able but some of the "this is
dangerous" is making me think twice.
No need to worry. You have a properly designed unvented cylinder from a
recognised brand, with all the expected controls and interlocks by the
sounds of it.
Yes in theory you can do dangerous things, but you would really have to
try, and defeat/disable multiple safety interlocks to even get close to
having a serious problem.
Any thoughts appreciated. Also if anyone know why I have 2 expansion
vessels and what they do that would fill a void in my understanding
too.
The two perform a similar function - but for different and unrelated
parts of the system. The one on the boiler allows for expansion of the
water in the radiator circuit. That's a sealed system with recirculating
(stagnant, dirty) water that goes through the boiler's primary heat
exchanger. The one on your cylinder is on the cold water mains input to
the store of DHW that you consume in the house.
Have a read of:
http://wiki.diyfaq.org.uk/index.php/...e d_or_vented
Then see the section on sealed systems for boilers:
http://wiki.diyfaq.org.uk/index.php/...AQ#Components:
Then the bit on unvented hot water systems like yours:
http://wiki.diyfaq.org.uk/index.php/Unvented_DHW
--
Cheers,
John.
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