Central Heating Expansion Tank Keeps filling Itself!
BraileTrail
system. In the loft are the usual cold water storage tank and heating
system expansion tank.
The overflows for the 2 tanks are combined in to one outlet that comes
out over next doors garage! Not a great idea and I will be changing that
soon.
Next door told me the overflow was running so I had a look in the loft
and indeed the expansion tank level was mm below the overflow pipe. The
valve was very old, scaled up and had no service valve. I fitted a
service valve and changed the valve for a modern diaphragm type and took
out about 8 litres of water while the system was cold.
Checked next day and the level was again mm below the overflow! Turned
off the service valve and took out another 8 litres of water. Next day
same again, the level is mm below the overflow.
I started to think that the old ball valve in the cold-water storage
tank was not working and that it was overflowing and, via the linked
overflows, filling the expansion tank. Looking at the fall on the
overflow pipe this is very unlikely, but couldn't think of anything
else. Today I changed the ball valve on the cold-water storage tank and
set the level about 75mm below the overflow, everything seems fine
there. Definitely not overflowing.
So, once again I drained 8 litres out of the heating expansion tank
while the system was cold and left it with the service valve closed.
Over a 5 hour period the level has risen by 30 mm with the heating and
water off and the service valve closed! The cold water storage tank
level is still 75mm below the overflow.
My only other thought is that the coil in the hot water tank has
corroded / burst and water is getting in to the system that way. Any
other ideas or thoughts on the matter would be appreciated.
BraileTrail
--
Tim Downie
"BraileTrail" <Braile...@home-free.demon.co.uk> wrote in message
news:FQHdTOCu...@home-free.demon.co.uk...
> OK, I have an old (25 years plus) semi-gravity gas fired central heating
> system. In the loft are the usual cold water storage tank and heating
> system expansion tank.
>
> The overflows for the 2 tanks are combined in to one outlet that comes out
> over next doors garage! Not a great idea and I will be changing that soon.
Could it be that it's the valve on your HW header tank that's leaking and
back filling the CH expansion tank through the siamesed outlets?
Tim
BraileTrail
In message <7puj89...@mid.individual.net>, Tim Downie
<timdow...@obvious.yahoo.co.uk> writes
>Could it be that it's the valve on your HW header tank that's leaking
>and back filling the CH expansion tank through the siamesed outlets?
It could be, please read on. ;)
BraileTrail
--
David WE Roberts
"BraileTrail" <Braile...@home-free.demon.co.uk> wrote in message
news:FQHdTOCu...@home-free.demon.co.uk...
> system. In the loft are the usual cold water storage tank and heating
> system expansion tank.
> My only other thought is that the coil in the hot water tank has corroded
> / burst and water is getting in to the system that way. Any other ideas or
> thoughts on the matter would be appreciated.
What are the relative levels of water in your hot water and central heating
expansion tanks?
If the heat exchanger coil in the hot water tank is leaking (which is not
uncommon in systems of that age) then as far as I can see this would over
time level the water in the two tanks as they have become directly
connected.
Presumably if it is a very small leak then the central heating system would
suck water in when cold (level in header tank goes down then comes up again
to match hot water header tank) then when heated rapidly by the boiler it
would expand and fill the small central heating header tank.
As you say, there doesn't seem to be any other way for water to get into the
central heating side of the system.
BraileTrail
In message <7pul24...@mid.individual.net>, David WE Roberts
<nos...@talk21.com> writes
>
>What are the relative levels of water in your hot water and central
>heating expansion tanks?
The expansion tank is sitting on the same plinth as the cold-water
storage tank so their bases are at the same level. The expansion
overflow level is below the full level and the overflow level of the
cold-water storage tank.
The overflow from the cold-water storage tank drops down vertically to
where it tee's in to the overflow from the expansion tank.
>If the heat exchanger coil in the hot water tank is leaking (which is
>not uncommon in systems of that age) then as far as I can see this
>would over time level the water in the two tanks as they have become
>directly connected.
That is my suspicion, of course it can't level it because the expansion
overflow pipe drains it off.
One thing I don't understand is that the expansion tank is just that, to
cope with the expansion when the water in the heating system gets hot,
I'm surprised (but pleased!!) that the water doesn't expand and come
over the top of the tank before the overflow can empty enough of it.
>Presumably if it is a very small leak then the central heating system
>would suck water in when cold (level in header tank goes down then
>comes up again to match hot water header tank) then when heated rapidly
>by the boiler it would expand and fill the small central heating header
>tank.
Again, that follows my reasoning. Sounds like a new tank may be in
order.
Can anyone think of anyway of testing the hypothesis before changing the
tank? So far there is no evidence of any leakage the other way, no brown
staining in the hot water or anything.
BraileTrail
--
Peter Parry
<Braile...@home-free.demon.co.uk> wrote:
>Can anyone think of anyway of testing the hypothesis before changing the
>tank? So far there is no evidence of any leakage the other way, no brown
>staining in the hot water or anything.
Turn off the water to the main tank and drain enough from a hot water
tap to bring the water level in the main tank below the level of that
in the expansion tank
Does the water level in the expansion tank now fall so both are more
or less level?
ransley
wrote:
> Tim,
>
> In message <7puj89Fta...@mid.individual.net>, Tim Downie
> <timdownie2...@obvious.yahoo.co.uk> writes
>
> >Could it be that it's the valve on your HW header tank that's leaking
> >and back filling the CH expansion tank through the siamesed outlets?
>
> It could be, please read on. ;)
>
> BraileTrail
>
> --
What feeds new water the boiler, is it an auto feed, they go bad. Shut
off the feeds. How many stories to the house, what is boiler water
level, I go up 35+ft but only need about 15lb of pressure in the
boiler when hot. Does the pressure relief on the boiler ever go off,
is there any indication on the boiler it does release, as in deposits
around the valve, lowering pressure may be the issue, you only need
enough pressure to get water to the highest radiator.
BraileTrail
<12ba52c0-3867-4fa8...@q2g2000yqd.googlegroups.com>,
ransley <Mark_R...@Yahoo.com> writes
>What feeds new water the boiler, is it an auto feed, they go bad. Shut
>off the feeds. How many stories to the house, what is boiler water
The expansion tank! It is a normal 2 story house.
>level, I go up 35+ft but only need about 15lb of pressure in the
>boiler when hot. Does the pressure relief on the boiler ever go off,
>is there any indication on the boiler it does release, as in deposits
>around the valve, lowering pressure may be the issue, you only need
>enough pressure to get water to the highest radiator.
It's an open-vented system, it's all at atmospheric pressure.
BraileTrail
--
Bob Minchin
to the tank is truly cut off.
Siphon water out of the expansion tank, or draw some off at the boiler
drain cock which ever is easiest.
If after some time the expansion tank fills up then you can be certain
you have a leak between primary and secondary circuits.
Quite a normal fault and unless you are very lucky, the new tank will
have inlets and outlets in different places so prepare for a fairly
significant job grovelling in your airing cupboard replumbing.
Fit a new long life immersion heater whilst you are at it as it will
almost certainly be corroded too.
A replacement tank fitted with sacrificial aluminium anodes will last
longer if you are planning to stay in the house 10yrs or more.
Good luck
Bob
BraileTrail
<pe...@wpp.ltd.uk> writes
>Turn off the water to the main tank and drain enough from a hot water
>tap to bring the water level in the main tank below the level of that
>in the expansion tank
>
>Does the water level in the expansion tank now fall so both are more
>or less level?
:)
Nice one Peter! My job for tomorrow morning. If I turn it off before we
shower in the morning then we wont even waste the water!
BraileTrail
--
The Wanderer
> So, once again I drained 8 litres out of the heating expansion tank
> while the system was cold and left it with the service valve closed.
> Over a 5 hour period the level has risen by 30 mm with the heating and
> water off and the service valve closed! The cold water storage tank
> level is still 75mm below the overflow.
>
> My only other thought is that the coil in the hot water tank has
> corroded / burst and water is getting in to the system that way. Any
> other ideas or thoughts on the matter would be appreciated.
If the service valve for the CH header is closed and the level is still
rising, there's only one place of common coupling between the two systems,
and that's the coil in the cylinder. Had exactly the same thing a year or
two back. My system is about 35 years old.
--
The Wanderer
Wine Improves with age. The older I get the better it tastes!
The Wanderer
Not necessary to prove where the problem lies. If the service valve for the
expansion tank is off and the level is still going up, there's only one
point of common coupling between the heating and domestic hot water
circuits, and that's the coil in the cylinder. New cylinder it is! :-(
--
The Wanderer
The future isn't what it used to be.
BraileTrail
In message <cMp_m.514$hP3...@newsfe30.ams2>, Bob Minchin
<Nos...@nospam.com> writes
>If after some time the expansion tank fills up then you can be certain
>you have a leak between primary and secondary circuits.
That much I know to be true already. With the service valve off the
level in the expansion tank rose 30mm in about 5 hours. The there is
clearly a leak some where and the most likely suspect is the hot tank
coils.
>Quite a normal fault and unless you are very lucky, the new tank will
>have inlets and outlets in different places so prepare for a fairly
>significant job grovelling in your airing cupboard replumbing.
Range will make a hot water cylinder with custom tapping's for you if
you ask. It doesn't cost anymore, but they are expensive cylinders
already.
BraileTrail
--
BraileTrail
<the.wa...@gmx.co.uk> writes
>Not necessary to prove where the problem lies. If the service valve for the
>expansion tank is off and the level is still going up, there's only one
>point of common coupling between the heating and domestic hot water
>circuits, and that's the coil in the cylinder. New cylinder it is! :-(
I hear what you and Bob say, but I would just like to "see" it before
launching in to a new cylinder.
BraileTrail
--
Peter Andrews
"Peter Parry" <pe...@wpp.ltd.uk> wrote in message
news:kc9kj5l8n0d3gqng3...@4ax.com...
Be aware that, at the moment, the flow is only from the hot water to the
central heating - if you change the water levels, such that the cold tank
level is lower than the expansion tank, you will CONTAMINATE your hot water
system with any chemical inhibitor that is in your CH system.
Peter
BraileTrail
<Braile...@home-free.demon.co.uk> writes
>Range will make a hot water cylinder with custom tapping's for you if
>you ask. It doesn't cost anymore, but they are expensive cylinders
>already.
Of course they can't do much about the heat exchanger tapping's I
suppose.
BraileTrail
--
BraileTrail
<p.an...@blueblueyonder.co.uk> writes
>Be aware that, at the moment, the flow is only from the hot water to the
>central heating - if you change the water levels, such that the cold tank
>level is lower than the expansion tank, you will CONTAMINATE your hot water
>system with any chemical inhibitor that is in your CH system.
Thanks for the warning, but I doubt that the flow is currently one way
only. Osmosis is going to ensure some mixing of the waters I would
think.
By lucky chance the system currently has no inhibitor I drained the
system to do some work several weeks ago and ran the system for a while
without just to check for leaks. I decided that I wanted to convert the
system to C-Plan to get independent control of the hot water and never
did put the inhibitor back in.
According to my neighbour the overflow leaked when the previous owners
were here and he couldn't get it sorted. So neither the work I did or
running the system without inhibitor for a short time has caused the
problem.
BraileTrail
--
geoff
<Braile...@home-free.demon.co.uk> writes
>In message <pjq_m.16652$S5.1...@newsfe18.ams2>, Peter Andrews
><p.an...@blueblueyonder.co.uk> writes
>>Be aware that, at the moment, the flow is only from the hot water to the
>>central heating - if you change the water levels, such that the cold tank
>>level is lower than the expansion tank, you will CONTAMINATE your hot water
>>system with any chemical inhibitor that is in your CH system.
>
>Thanks for the warning, but I doubt that the flow is currently one way
>only. Osmosis is going to ensure some mixing of the waters I would
>think.
Osmosis ?
An interesting concept
total bollocks, but interesting
>
>By lucky chance the system currently has no inhibitor I drained the
>system to do some work several weeks ago and ran the system for a while
>without just to check for leaks. I decided that I wanted to convert the
>system to C-Plan to get independent control of the hot water and never
>did put the inhibitor back in.
>
>According to my neighbour the overflow leaked when the previous owners
>were here and he couldn't get it sorted. So neither the work I did or
>running the system without inhibitor for a short time has caused the
>problem.
>
>BraileTrail
>
--
geoff
BraileTrail
writes
>Osmosis ?
>
>An interesting concept
It is, fascinating.
>total bollocks, but interesting
Rather harsh! Anything else useful to add?
How about diffusion then?
BraileTrail
--
Dave Liquorice
> It's an open-vented system, it's all at atmospheric pressure.
Well not quite, the pressure in the system at the bottom has the head
of water to the level in the expansion tank as well. Reducing to
atmospheric pressure at the level of the water in the tank.
This is why the flow with a holed coil in a cylinder is generally
only one way from the HW system into the primary. The cold water
storeage tank is normally much larger than the heating header tank
thus the level of water in the CW tank is higher than that in the
heating header tank. Thus the pressure in the coil is lower than that
in the HW tank, may only be a foot head of water but it's enough to
ensure the unidirectional flow.
--
Cheers
Dave.
geoff
<Braile...@home-free.demon.co.uk> writes
>In message <AhfjeGVb...@demon.co.uk>, geoff <ra...@kateda.org>
>writes
>>Osmosis ?
>>
>>An interesting concept
>
>It is, fascinating.
>
>>total bollocks, but interesting
>
>Rather harsh! Anything else useful to add?
Total AND absolute bollocks
how's that?
>
>How about diffusion then?
What diffusion ?
There is no semi permeable membrane, there is no diffusion between the
CH and DHW
If you have CH water in the DHW, it's called a LEAK
if you really don't understand, better get a man in
>
>BraileTrail
>
--
geoff
Roger Mills
BraileTrail <Braile...@home-free.demon.co.uk> wrote:
>
> By lucky chance the system currently has no inhibitor I drained the
> system to do some work several weeks ago and ran the system for a
> while without just to check for leaks. I decided that I wanted to
> convert the system to C-Plan to get independent control of the hot
> water and never did put the inhibitor back in.
>
Since you're going have to replace your hot cylinder, why not get a new one
with a quick recovery coil and - at the same time - convert your system to
an S-Plan or Y-Plan rather than C-Plan - and get much faster hot water than
you get with your gravity system, as well as the other advantages of a
fully-pumped system?
--
Cheers,
Roger
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BraileTrail
<watt....@googlemail.com> writes
>Since you're going have to replace your hot cylinder, why not get a new one
>with a quick recovery coil and - at the same time - convert your system to
>an S-Plan or Y-Plan rather than C-Plan - and get much faster hot water than
>you get with your gravity system, as well as the other advantages of a
>fully-pumped system?
We got some quotes after we moved in to change the boiler and do just
that with either a) replace the cylinder with a fast recovery model or
b) replace the cylinder and storage tanks by a thermal store.
The cost was somewhat higher than expected so I started doing little
bits myself to keep the system going. We are now at the point where we
have to decide whether to keep patching things until the boiler finally
packs up or go for the works now.
BraileTrail
--
Grimly Curmudgeon
drugs began to take hold. I remember BraileTrail
<Braile...@home-free.demon.co.uk> saying something like:
>>What feeds new water the boiler, is it an auto feed, they go bad. Shut
>>off the feeds. How many stories to the house, what is boiler water
>
>The expansion tank! It is a normal 2 story house.
You must excuse him, he's an American.
Grimly Curmudgeon
something like:
>>
>>Thanks for the warning, but I doubt that the flow is currently one way
>>only. Osmosis is going to ensure some mixing of the waters I would
>>think.
>
>Osmosis ?
70s band, iirc.
>An interesting concept
>
>total bollocks,
Indeed.
>but interesting
Not even that.