I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

After reviewing several posts to this news group I read that the most
obvious problem is the poor flow from the cold header to the cylinder.
Most posts seem to suggest upgrading this pipework to 28mm, reducing
the number of elbows with bends, etc...

I have a couple of questions I hope someone can help with:

1: I didn't have this problem before when the cold header was in the
loft, and the hot cylinder was on the landing. am I right to think that
the flow from the cold header to the cylinder was under much higher
pressure because of the head of water. now both cold header and hot
cylinder are in the loft the head of water has been reduced
significantly from what is was before.

2: even if I upgrade the pipe to 28mm, I'm not aware of a fitting that
connects 28mm pipe to the 1inch cylinder connector. would I have to
convert the 28mm down to 22mm to connect it to the cylinder, and
therefore wouldn't this still be the bottleneck?

thanks for any advice or links to sites that sell the appropriate
connectors

wrote in message
ups.com...
I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

After reviewing several posts to this news group I read that the most
obvious problem is the poor flow from the cold header to the cylinder.
Most posts seem to suggest upgrading this pipework to 28mm, reducing
the number of elbows with bends, etc...

I have a couple of questions I hope someone can help with:

1: I didn't have this problem before when the cold header was in the
loft, and the hot cylinder was on the landing. am I right to think that
the flow from the cold header to the cylinder was under much higher
pressure because of the head of water. now both cold header and hot
cylinder are in the loft the head of water has been reduced
significantly from what is was before.

2: even if I upgrade the pipe to 28mm, I'm not aware of a fitting that
connects 28mm pipe to the 1inch cylinder connector. would I have to
convert the 28mm down to 22mm to connect it to the cylinder, and
therefore wouldn't this still be the bottleneck?

thanks for any advice or links to sites that sell the appropriate
connectors

Replace with 28mm and keep elbows to a minium. Bend if you can. 28mm
connectors are standard. http://www.bes.co.uk

You may want to fit a 28mm open vent too. This means more water in the pipe
to be dragged through the draw-off before reaching any air, then the cold
feed may have settled out. Also use full-bore isolation valves on the 28mm
pipe.

just as a test before replacing all with 28mm I connected up the cold
water feed from the cold header to the bottom of the cylinder also. (I
have two tank connectors on the cold header, 1 for hot and 1 for cold).
so essentially now both are feeding the bottom of the cylinder.

however, the vent pipe still easily sucks up water from a glass when
the bath hot tap is on full.

surely 2x22mm are better than 1x28mm so I'm stuck again since I'm not
convinved that 28mm pipe will make the situation any better.



Doctor Drivel wrote:
wrote in message
ups.com...
I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

After reviewing several posts to this news group I read that the most
obvious problem is the poor flow from the cold header to the cylinder.
Most posts seem to suggest upgrading this pipework to 28mm, reducing
the number of elbows with bends, etc...

I have a couple of questions I hope someone can help with:

1: I didn't have this problem before when the cold header was in the
loft, and the hot cylinder was on the landing. am I right to think that
the flow from the cold header to the cylinder was under much higher
pressure because of the head of water. now both cold header and hot
cylinder are in the loft the head of water has been reduced
significantly from what is was before.

2: even if I upgrade the pipe to 28mm, I'm not aware of a fitting that
connects 28mm pipe to the 1inch cylinder connector. would I have to
convert the 28mm down to 22mm to connect it to the cylinder, and
therefore wouldn't this still be the bottleneck?

thanks for any advice or links to sites that sell the appropriate
connectors

Replace with 28mm and keep elbows to a minium. Bend if you can. 28mm
connectors are standard. http://www.bes.co.uk

You may want to fit a 28mm open vent too. This means more water in the pipe
to be dragged through the draw-off before reaching any air, then the cold
feed may have settled out. Also use full-bore isolation valves on the 28mm
pipe.

does it matter if at the top of the hot water cylinder the 22mm pipe
that exists the cylinder goes in to a tee whose other 2 connections run
left and right (i.e. the pipe carrying the hot water to downstairs runs
horizontal until it bends down 90degrees and goes through the roof. the
other part of the tee again runs horizontal (well slight upwards
really, until it bends upwards and then over and cold header tank as
normal.

by theory is that since most diagrams and installations I've ever seen
have a tee, but is is positioned such that the vent pipe comes out of
the top of the tee, and the hot water exists the tee sideways, perhaps
there is a problem with my arrangement.

could the fact that both the hot water to downstairs and the initial
part of the vent part exist the tee horizontally mean that when the
bath hot tap is on full there is a sucking force applied to the water
in the vent pipe ?

I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

wrote:
just as a test before replacing all with 28mm I connected up the cold
water feed from the cold header to the bottom of the cylinder also. (I
have two tank connectors on the cold header, 1 for hot and 1 for cold).
so essentially now both are feeding the bottom of the cylinder.

however, the vent pipe still easily sucks up water from a glass when
the bath hot tap is on full.

surely 2x22mm are better than 1x28mm so I'm stuck again since I'm not
convinved that 28mm pipe will make the situation any better.



Doctor Drivel wrote:
wrote in message
ups.com...
I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

After reviewing several posts to this news group I read that the most
obvious problem is the poor flow from the cold header to the cylinder.
Most posts seem to suggest upgrading this pipework to 28mm, reducing
the number of elbows with bends, etc...

I have a couple of questions I hope someone can help with:

1: I didn't have this problem before when the cold header was in the
loft, and the hot cylinder was on the landing. am I right to think that
the flow from the cold header to the cylinder was under much higher
pressure because of the head of water. now both cold header and hot
cylinder are in the loft the head of water has been reduced
significantly from what is was before.

2: even if I upgrade the pipe to 28mm, I'm not aware of a fitting that
connects 28mm pipe to the 1inch cylinder connector. would I have to
convert the 28mm down to 22mm to connect it to the cylinder, and
therefore wouldn't this still be the bottleneck?

thanks for any advice or links to sites that sell the appropriate
connectors

Replace with 28mm and keep elbows to a minium. Bend if you can. 28mm
connectors are standard. http://www.bes.co.uk

You may want to fit a 28mm open vent too. This means more water in the pipe
to be dragged through the draw-off before reaching any air, then the cold
feed may have settled out. Also use full-bore isolation valves on the 28mm
pipe.

The message .com
from contains these words:


I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

That is your basic problem.

The vent pipe on the hot outlet means that the run from cold tank to hot
tap is effectively 2 independent parts and if the lower run can pass
water faster than the upper run then air will be drawn in. The pressure
head driving the cold water into the tank can be no more than the
difference in height between the water surface in the cold tank and the
vent junction. The pressure driving the water into the bath is the
height difference between the water level in the vent pipe (maximum when
the level drops to the vent junction) and the bath tap and parity is
reached when the water level in the vent pipe (by then actually in the
hot tap supply pipe) has reduced the head sufficiently for the flows to
match.

You are stuck with the connections you have but every little improvement
will help the flow into the tank. Removing elbows and increasing to 28mm
will both help. There are tables around that will tell you what flow you
should get with various lengths of pipe at various heads and the
equivalent length to add on for each fitting but it seems to me that the
head disparity is so great that you will have to put some restriction in
the feed to the hot tap to avoid drawing in air. A gate valve would do.
Experiment till air is not drawn in and then take off and hide the
handle.

You may be getting the same problem on some or all of your other hot
taps but have not noticed it as full on is less likely on those taps.

One final point. Have you asked yourself does it actually matter if air
is drawn into the hot supply in that manner. I am not entirely sure it
does but it might depend on what is likely to be sucked in with it.

Don't listen to Dribble. He is permanently in my killfile but I couldn't
help noticing he advised you to increase the diameter of the vent pipe.
You won't notice the fraction of a second difference the increased
reservoir in the vent pipe delivers before it starts to feed air.

--
Roger Chapman

"Roger" wrote in message
k...
The message .com
from contains these words:


I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

That is your basic problem.

The vent pipe on the hot outlet

Roger, you haven't half a clue what you are on about. You are also a big
guesser too.

thanks Roger, appreciate the long detailed response.

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

before I moved the hot cylinder to the loft I had about 6-7 feet head
of water from the top of cold header to the top of the cylinder, and
the head of water to the bath tap would havev been, say, 8-9 feet -
i.e. not much difference.

have I got that all correct?

I did try previously only partially opening the bath hot tap and it did
not seem to have an air in it, so you comment about essentially
restricting the flow to the hot table seems to marry up with that test
I did.

why did I decide to move it to the loft.......


Roger wrote:
The message .com
from contains these words:


I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

That is your basic problem.

The vent pipe on the hot outlet means that the run from cold tank to hot
tap is effectively 2 independent parts and if the lower run can pass
water faster than the upper run then air will be drawn in. The pressure
head driving the cold water into the tank can be no more than the
difference in height between the water surface in the cold tank and the
vent junction. The pressure driving the water into the bath is the
height difference between the water level in the vent pipe (maximum when
the level drops to the vent junction) and the bath tap and parity is
reached when the water level in the vent pipe (by then actually in the
hot tap supply pipe) has reduced the head sufficiently for the flows to
match.

You are stuck with the connections you have but every little improvement
will help the flow into the tank. Removing elbows and increasing to 28mm
will both help. There are tables around that will tell you what flow you
should get with various lengths of pipe at various heads and the
equivalent length to add on for each fitting but it seems to me that the
head disparity is so great that you will have to put some restriction in
the feed to the hot tap to avoid drawing in air. A gate valve would do.
Experiment till air is not drawn in and then take off and hide the
handle.

You may be getting the same problem on some or all of your other hot
taps but have not noticed it as full on is less likely on those taps.

One final point. Have you asked yourself does it actually matter if air
is drawn into the hot supply in that manner. I am not entirely sure it
does but it might depend on what is likely to be sucked in with it.

Don't listen to Dribble. He is permanently in my killfile but I couldn't
help noticing he advised you to increase the diameter of the vent pipe.
You won't notice the fraction of a second difference the increased
reservoir in the vent pipe delivers before it starts to feed air.

--
Roger Chapman

wrote in message
oups.com...
does it matter if at the top of the hot water cylinder the 22mm pipe
that exists the cylinder goes in to a tee whose other 2 connections run
left and right (i.e. the pipe carrying the hot water to downstairs runs
horizontal until it bends down 90degrees and goes through the roof. the
other part of the tee again runs horizontal (well slight upwards
really, until it bends upwards and then over and cold header tank as
normal.

by theory is that since most diagrams and installations I've ever seen
have a tee, but is is positioned such that the vent pipe comes out of
the top of the tee, and the hot water exists the tee sideways, perhaps
there is a problem with my arrangement.

could the fact that both the hot water to downstairs and the initial
part of the vent part exist the tee horizontally mean that when the
bath hot tap is on full there is a sucking force applied to the water
in the vent pipe ?

I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

From the cylinder draw-off connection have a bend, then a length of pipe
then a tee. from the tee go to the taps. The other part of tee is the open
vent. Don't go up and over the cylinder from the draw-off on the cylinder
and have a tee on this just above the cylinder. You may want to have the
draw-off from the cylinder in 28mm then a 22mm vent pipe at the tee.

Two 22mm pipes still are entering the cylinder via one 22mm connection of
the cylinder. It may be worth your while having a length of 28mm plastic
pipe from the tank to cylinder to avoid elbows, but only use compression
joints, not push-fits and use a full-bore 28mm isolation valve.

wrote in message
oups.com...

thanks Roger, appreciate the long detailed response.

Yes, one based on no experince.

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

From the cold tank to the hot tap you have a pipe. In between this pipe you
have a fat pipe, called a cylinder. This fat pipe can be heated up. The
less restrictions you have to flow in the complete run of pipe, inc'
cylidner, to the tap, the problem will disappear.

so you're saying that because the flow from the cold header to the tank
is not large enough, when the hot tap is turned fully on it is dragging
the water (and then air) from the vent pipe? I'm not certain I
understand this? the pipes from the loft to the hot water taps are all
22mm also.

so this big pipe as you describe it is all 22mm (in fact from header to
cylinder its two 22mm, although I'd concede that since they join in a
22mm tee before entering the bottom of the cylinder the flow is still
limited to 22mm) then why is additional water (and air) sucked from the
vent pipe?

thanks for your replies also Doctor Drivel, any/all help ideas are
appreciated on this one

Doctor Drivel wrote:
wrote in message
oups.com...

thanks Roger, appreciate the long detailed response.

Yes, one based on no experince.

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

From the cold tank to the hot tap you have a pipe. In between this pipe you
have a fat pipe, called a cylinder. This fat pipe can be heated up. The
less restrictions you have to flow in the complete run of pipe, inc'
cylidner, to the tap, the problem will disappear.

so you think that fact that I have a tee in a T shape (i.e. two
horizontals feeds and one feed at the bottom) directly above the hot
take off is an issue? most diagrams I see have the T on its side, with
the flow to the hot taps leave this T on the horizontal and the vent
leaving the T from the top (the take off from the cylinder enters this
T from below)

Doctor Drivel wrote:
wrote in message
oups.com...
does it matter if at the top of the hot water cylinder the 22mm pipe
that exists the cylinder goes in to a tee whose other 2 connections run
left and right (i.e. the pipe carrying the hot water to downstairs runs
horizontal until it bends down 90degrees and goes through the roof. the
other part of the tee again runs horizontal (well slight upwards
really, until it bends upwards and then over and cold header tank as
normal.

by theory is that since most diagrams and installations I've ever seen
have a tee, but is is positioned such that the vent pipe comes out of
the top of the tee, and the hot water exists the tee sideways, perhaps
there is a problem with my arrangement.

could the fact that both the hot water to downstairs and the initial
part of the vent part exist the tee horizontally mean that when the
bath hot tap is on full there is a sucking force applied to the water
in the vent pipe ?

I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

From the cylinder draw-off connection have a bend, then a length of pipe
then a tee. from the tee go to the taps. The other part of tee is the open
vent. Don't go up and over the cylinder from the draw-off on the cylinder
and have a tee on this just above the cylinder. You may want to have the
draw-off from the cylinder in 28mm then a 22mm vent pipe at the tee.

Two 22mm pipes still are entering the cylinder via one 22mm connection of
the cylinder. It may be worth your while having a length of 28mm plastic
pipe from the tank to cylinder to avoid elbows, but only use compression
joints, not push-fits and use a full-bore 28mm isolation valve.

The message .com
from contains these words:

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

before I moved the hot cylinder to the loft I had about 6-7 feet head
of water from the top of cold header to the top of the cylinder, and
the head of water to the bath tap would havev been, say, 8-9 feet -
i.e. not much difference.

have I got that all correct?

It is an unusual installation anyway if the cold water tank was not in
the loft to start with but if I understand you correctly what you have
done is to increase the head to your bath tap by a full storey while
maintaining the height difference between hot tank and cold tank. Given
the figures you quote that is probably somewhere around 10 feet so
instead of having 6 foot of head driving the cold water into the hot
tank and 1 - 2 foot of head sucking the hot water out you have 6 foot of
head driving the water in and 11 - 12 foot of head sucking it out. If
you have plumbed your bath hot tap in 22 mm pipe then I can't see how
you can resolve your problem without restricting the flow to the tap but
that is just a gut feeling. I don't have the tables to resolve the
issue.

--
Roger Chapman

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.


Roger wrote:
The message .com
from contains these words:

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

before I moved the hot cylinder to the loft I had about 6-7 feet head
of water from the top of cold header to the top of the cylinder, and
the head of water to the bath tap would havev been, say, 8-9 feet -
i.e. not much difference.

have I got that all correct?

It is an unusual installation anyway if the cold water tank was not in
the loft to start with but if I understand you correctly what you have
done is to increase the head to your bath tap by a full storey while
maintaining the height difference between hot tank and cold tank. Given
the figures you quote that is probably somewhere around 10 feet so
instead of having 6 foot of head driving the cold water into the hot
tank and 1 - 2 foot of head sucking the hot water out you have 6 foot of
head driving the water in and 11 - 12 foot of head sucking it out. If
you have plumbed your bath hot tap in 22 mm pipe then I can't see how
you can resolve your problem without restricting the flow to the tap but
that is just a gut feeling. I don't have the tables to resolve the
issue.

--
Roger Chapman

The message . com
from contains these words:

thanks Roger, appreciate the long detailed response.

Yes, one based on no experince.

As I said before don't listen to Dribble. Unless you know the subject
well you can't tell whether anything he is saying has any value, and if
you do know the subject you don't need to bother reading the rubbish
Dribble routinely puts out. The most that can be said for Dribble is
that he is very good at cutting and pasting but when it comes to
thinking problems through you can almost guarantee he will get it wrong.

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

From the cold tank to the hot tap you have a pipe. In between this
pipe you
have a fat pipe, called a cylinder. This fat pipe can be heated up. The
less restrictions you have to flow in the complete run of pipe, inc'
cylidner, to the tap, the problem will disappear.

So according to Dribble if you upgraded the pipe to the hot tap from
22mm to 28mm your problem would at least be reduced. The plain truth is
that that would just make matters worse.

--
Roger Chapman

"Roger" wrote in message
k...
The message . com
from contains these words:

thanks Roger, appreciate the long detailed response.

Yes, one based on no experince.

As

Roger, you are pure amateur and an idiot to boot. I am no amateur. To the
OP, don't take too much of what he says seriously at all. He is a know loon.

The message .com
from contains these words:

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

Which is what I had thought you had done in the first place before you
quoted figures that appeared to say different.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.

It is. What you have to remember is that the vent pipe splits the run
from header tank to tap so that if the resistence to flow is greater in
the first part of the run the vent pipe allows the water in the second
part of the run to escape quicker than it is replenished. The crucial
point is not actually the top of the cylinder but the junction with the
vent pipe. I think the bath tap, even when fully open, will restrict
flow to a certain extent but, other things being equal, you need the
same head between cold water level and junction as between junction and
tap.

So you have got at the most 18 inches of head driving the water into the
tank and perhaps 9 foot of head sucking the water out. If your header
tank previously sat on the joints you should at least be getting a
greater flow of water at the hot tap than you had before.

Do you have room in the loft to raise the header tank further? That too
will improve matters.

--
Roger Chapman

does this mean that moving a hot water cylinder to the loft is
fundementally flawed then? noone's loft is going to allow the cold
header to have a huge head over the cylinder in the loft.


Roger wrote:
The message .com
from contains these words:

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

Which is what I had thought you had done in the first place before you
quoted figures that appeared to say different.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.

It is. What you have to remember is that the vent pipe splits the run
from header tank to tap so that if the resistence to flow is greater in
the first part of the run the vent pipe allows the water in the second
part of the run to escape quicker than it is replenished. The crucial
point is not actually the top of the cylinder but the junction with the
vent pipe. I think the bath tap, even when fully open, will restrict
flow to a certain extent but, other things being equal, you need the
same head between cold water level and junction as between junction and
tap.

So you have got at the most 18 inches of head driving the water into the
tank and perhaps 9 foot of head sucking the water out. If your header
tank previously sat on the joints you should at least be getting a
greater flow of water at the hot tap than you had before.

Do you have room in the loft to raise the header tank further? That too
will improve matters.

--
Roger Chapman

The message .com
from contains these words:

does this mean that moving a hot water cylinder to the loft is
fundementally flawed then? noone's loft is going to allow the cold
header to have a huge head over the cylinder in the loft.

No, but you have to cut your cloth to suit yur coat. As I said before
you will have a greater flow at the hot tap now than you would have with
your previous setup and that would continue to be the case if you put a
gate valve in the lower run and throttled the flow down till you got no
air admitted.

Some lofts at least would have more headroom than yours and thus more scope.

--
Roger Chapman

"Roger" wrote in message
k...

It is. What you have to remember is that the vent pipe splits the run
from header tank to tap so that if the resistence to flow is greater in
the first part of the run the vent pipe allows the water in the second
part of the run to escape quicker than it is replenished.

At last you got it Roger. 10/10. V good. That is why the cold feed should
be a large bore unrestricted pipe to give "flow" to compensate for the low
head.

In article . com,
writes

I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

Just so I understand: have you extended the vent pipe to the new cold
header tank position?

--
(\__/)
(='.'=) This is Bunny. Copy and paste Bunny into your
(")_(") signature to help him gain world domination.

I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

This confirms nothing. The vent pipe WILL suck in any installation. It only
matters if the pressure difference between the cylinder and vent pipe outlet
is enough to suck so far that the water column entirely disappears so that
air enters the system. I see nothing to suggest that this has happened. The
symptom you are looking for isn't reduced pressure and a bit of sucking at
the vent (which will happen in any system, including a healthy one), but
funny noises and entrained air in the hot water stream.

Christian.

wrote:

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.

When we moved in here, the hot water system was very similar to what you
have described here, and yes, it did suck gob loads of air into the system!

One simple fix you could try would be to arrange the hot out from the
cylinder in the way some shower pump manufacturers suggest for setups
that are not using dedicated flanges etc:


|V|
| |
\ \
\ \
/ \
/ /\ \
/ / \ \
/H/ \ \
__| |__
-- --
- -
| |
| |
| |
| |
| |
| |
| |
|___________|

Hot water feed come striaght up from top connector and then makes a 45
degree bend. You then have a couple of feet of pipe at this angle before
it bends straight again and goes off to do the normal vent thing.

The hot water supply to the taps (H) is then teed off the underside of
the slanted section.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

the vent pipe comes out of the top of the cylinder (via a tee), and
runs via a slight slope up to and over the cold water storage tank

Mike Tomlinson wrote:
In article . com,
writes

I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

Just so I understand: have you extended the vent pipe to the new cold
header tank position?

--
(\__/)
(='.'=) This is Bunny. Copy and paste Bunny into your
(")_(") signature to help him gain world domination.

Christian, I did wonder if other people's vent pipe sucked in water -
so thanks as you seem to confirm this.

actually my first attempt at fixing this was to increase the amount of
water in the vent pipe (it was only about 12-14" before) and I did this
by running the vent pipe at a slight include along the roof line, and
then back again, again at a slight upwards incline, and then over the
cold water header. this meant I had a pipe of vent pipe of around 8ft
of water in it, albeit on its side. I confirmed how much water was in
this by holding the pipe, it felt hot for about 8ft.

however, yes I am definitely getting air sucked in to the system as I
have an air vent at a point downstair (between the cylinder and the
bath tap) and this continually has to be drained of air.


Christian McArdle wrote:
I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

This confirms nothing. The vent pipe WILL suck in any installation. It only
matters if the pressure difference between the cylinder and vent pipe outlet
is enough to suck so far that the water column entirely disappears so that
air enters the system. I see nothing to suggest that this has happened. The
symptom you are looking for isn't reduced pressure and a bit of sucking at
the vent (which will happen in any system, including a healthy one), but
funny noises and entrained air in the hot water stream.

Christian.

it seems to me as though I need to update the run from the cold header
to the bottom of the cylinder in 28mm (and I know not everyone is in
agreement on this)

I've been told by a plumbers merchant that the bore size of a 28mm-1"
brass cylinder connector is 28mm, so, if my calculations are correct,
if I change all of this to 28mm (as I've been told to do in the
newsgroup, thanks, and by others) then it should double the flow to the
bottom of the cylinder.

the reason for me saying that the bore is 28mm is that my fear was that
the bore of the 28mm-1" cylinder connector and the bore of a 22mm-1"
cylinder connector would be the same, so moving to 28mm would still be
restricted when it entered the cylinder. but my fears were not correct.

I'm gonna try moving to 28mm and see if that fixes it before I do
anything else.

wrote:
Christian, I did wonder if other people's vent pipe sucked in water -
so thanks as you seem to confirm this.

actually my first attempt at fixing this was to increase the amount of
water in the vent pipe (it was only about 12-14" before) and I did this
by running the vent pipe at a slight include along the roof line, and
then back again, again at a slight upwards incline, and then over the
cold water header. this meant I had a pipe of vent pipe of around 8ft
of water in it, albeit on its side. I confirmed how much water was in
this by holding the pipe, it felt hot for about 8ft.

however, yes I am definitely getting air sucked in to the system as I
have an air vent at a point downstair (between the cylinder and the
bath tap) and this continually has to be drained of air.


Christian McArdle wrote:
I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

This confirms nothing. The vent pipe WILL suck in any installation. It only
matters if the pressure difference between the cylinder and vent pipe outlet
is enough to suck so far that the water column entirely disappears so that
air enters the system. I see nothing to suggest that this has happened. The
symptom you are looking for isn't reduced pressure and a bit of sucking at
the vent (which will happen in any system, including a healthy one), but
funny noises and entrained air in the hot water stream.

Christian.

however, yes I am definitely getting air sucked in to the system as I
have an air vent at a point downstair (between the cylinder and the
bath tap) and this continually has to be drained of air.

OK.

The basic way this thing works is that when you turn a tap on, the pressure
in the hot water cylinder drops, in proportion to the speed of the water
flow.

Your choices a

1. Slow the speed of water (probably not a popular choice).
2. Increase the supply of cold water to reduce the pressure drop.
3. Increase the height of the vent pipe, so that a higher pressure can be
present without sucking dry.

Sounds like you are going with option 2, which is sensible. If this doesn't
work, try option 3, by running the vent higher. If the vent goes only a foot
or so before bending over the cistern, it won't cope with a reasonable
pressure differential.

Christian.

"John Rumm" wrote in message
...
wrote:

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.

When we moved in here, the hot water system was very similar to what you
have described here, and yes, it did suck gob loads of air into the
system!

One simple fix you could try would be to arrange the hot out from the
cylinder in the way some shower pump manufacturers suggest for setups that
are not using dedicated flanges etc:

Yep. If the uprating of the cold feed does not do it a £15 Surrey flange
will. If a 1" tapping on the cylidner draw-off then get a 1" Surrey Flange.

John Rumm wrote:
wrote:

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.

When we moved in here, the hot water system was very similar to what you
have described here, and yes, it did suck gob loads of air into the system!

One simple fix you could try would be to arrange the hot out from the
cylinder in the way some shower pump manufacturers suggest for setups
that are not using dedicated flanges etc:


|V|
| |
\ \
\ \
/ \
/ /\ \
/ / \ \
/H/ \ \
__| |__
-- --
- -
| |
| |
| |
| |
| |
| |
| |
|___________|

Hot water feed come striaght up from top connector and then makes a 45
degree bend. You then have a couple of feet of pipe at this angle before
it bends straight again and goes off to do the normal vent thing.

The hot water supply to the taps (H) is then teed off the underside of
the slanted section.

That's to prevent air bubbles collecting in any horizontal pipe runs
and being sucked through the pump. I doubt it wil help in this
situation.

MBQ

wrote in message
ps.com...
the vent pipe comes out of the top of the cylinder (via a tee), and
runs via a slight slope up to and over the cold water storage tank

Get the tee away from the cylinder. Come off the cylinder with an elbow.
Horizontal to the point where the draw-off drops to the rooms below. Bend
the pipe here down to the room below. Just before the downwards bend insert
the tee. The vent must go right up to the roof and down to the cold tank.

are you saying that extending the height of the vent pipe before it
bends down above the cold header will make a difference?

someone else suggested this, but it didn't seem to make sense since
even if I extend the vent pipe the water level in the vent pipe will
remain at the same level (the level of the water in the cold header,
right?)


Christian McArdle wrote:
however, yes I am definitely getting air sucked in to the system as I
have an air vent at a point downstair (between the cylinder and the
bath tap) and this continually has to be drained of air.

OK.

The basic way this thing works is that when you turn a tap on, the pressure
in the hot water cylinder drops, in proportion to the speed of the water
flow.

Your choices a

1. Slow the speed of water (probably not a popular choice).
2. Increase the supply of cold water to reduce the pressure drop.
3. Increase the height of the vent pipe, so that a higher pressure can be
present without sucking dry.

Sounds like you are going with option 2, which is sensible. If this doesn't
work, try option 3, by running the vent higher. If the vent goes only a foot
or so before bending over the cistern, it won't cope with a reasonable
pressure differential.

Christian.

someone else suggested this, but it didn't seem to make sense since
even if I extend the vent pipe the water level in the vent pipe will
remain at the same level (the level of the water in the cold header,
right?)

You're right. I had a brain fart. It helps in a different situation not
related to your problem.

Basically, that option turns into raising the cold water cistern at high as
possible, so that it can cope with a higher pressure differential.

Christian.

I have 'extended' the vent pipe by running it for a long length at a
slight incline, and then back again, still at a slight include, back to
the cold header. so there is more water in the pipe, even though its
not a vertical pipe.

however, its not just the initial dip in pressure that sucks air in.
air is sucked in while the bath hot tap is on, not much, but enough to
cause problems. so even if the vent pipe was 30m high eventually (if I
ran a full bath) the water would be sucked out, and air would then be
introduced.

Christian McArdle wrote:
someone else suggested this, but it didn't seem to make sense since
even if I extend the vent pipe the water level in the vent pipe will
remain at the same level (the level of the water in the cold header,
right?)

You're right. I had a brain fart. It helps in a different situation not
related to your problem.

Basically, that option turns into raising the cold water cistern at high as
possible, so that it can cope with a higher pressure differential.

Christian.

however, its not just the initial dip in pressure that sucks air in.
air is sucked in while the bath hot tap is on, not much, but enough to
cause problems. so even if the vent pipe was 30m high eventually (if I
ran a full bath) the water would be sucked out, and air would then be
introduced.

Indeed. The height of the water column determines how much pressure it can
resist (1m height resists about 0.1 bar of pressure differential). Making
the pipe larger so it contains more water won't really help but will only
delay the onset slightly.

Christian.

On 21 Sep 2006 04:14:28 -0700, wrote:

however, yes I am definitely getting air sucked in to the system as I
have an air vent at a point downstair (between the cylinder and the
bath tap) and this continually has to be drained of air.

Ah but is that air actually being sucked in down the vent or is it the
air relased from the water when it is heated?

The vent should rise vertically from the top of the HW cylinder for a
short distance and feeds T'd from this vertical section. The released air
will then rise up into the bottom of the vent pipe. If the top connection
to the tank goes to an elbow and short horizontal section with the HW
feed and vent T's to the end the released air will collect in the
horizontal section and be drawn by the water flow into the system and out
of the taps.

--
Cheers
Dave. pam is missing e-mail

wrote in message
ups.com...

John Rumm wrote:
wrote:

just to clarify, all I've done is move the hot water cylinder from the
landing to the loft. in the loft I have built a wooden platform and sat
the cold header tank (that was always in the loft) on to the platform.
the hot water cylinder sits on the joists (on a think piece of wood to
spread the load over 6 joists) and the bottom of the cold header is now
just above the top of the hot water cylinder.

the head of water above the top of the hot water cylinder must be
around18 inches (essentially this is the height of the cold water tank
since the water in the cold header is only a few inches from the top
when full). the head of water for the hot bath tap must now be
something like 8 feet (to the top of the water in the cold header)

I'm still unsure if this vast difference in the head of water is the
cause of the problem or not. all the plumbing is 22mm, right the way to
the bath tap.

When we moved in here, the hot water system was very similar to what you
have described here, and yes, it did suck gob loads of air into the
system!

One simple fix you could try would be to arrange the hot out from the
cylinder in the way some shower pump manufacturers suggest for setups
that are not using dedicated flanges etc:


|V|
| |
\ \
\ \
/ \
/ /\ \
/ / \ \
/H/ \ \
__| |__
-- --
- -
| |
| |
| |
| |
| |
| |
| |
|___________|

Hot water feed come striaght up from top connector and then makes a 45
degree bend. You then have a couple of feet of pipe at this angle before
it bends straight again and goes off to do the normal vent thing.

The hot water supply to the taps (H) is then teed off the underside of
the slanted section.

That's to prevent air bubbles collecting in any horizontal pipe runs
and being sucked through the pump. I doubt it wil help in this
situation.

You have to understand how a Surrey flange works.

The message om
from "Dave Liquorice" contains these words:

Ah but is that air actually being sucked in down the vent or is it the
air relased from the water when it is heated?

I am convinced that the air just has to be sucked in down the vent pipe.
There isn't sufficient head (short by perhaps as much as 6 foot) to
drive water through the tank fast enough to satisfy the outlet at full
flow. Once the reservoir in the vent pipe is exhausted (by the time the
tap is turned full on) air is bound to get into the main run.

--
Roger Chapman

wrote:

thanks Roger, appreciate the long detailed response.

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

before I moved the hot cylinder to the loft I had about 6-7 feet head
of water from the top of cold header to the top of the cylinder, and
the head of water to the bath tap would havev been, say, 8-9 feet -
i.e. not much difference.

have I got that all correct?

I did try previously only partially opening the bath hot tap and it did
not seem to have an air in it, so you comment about essentially
restricting the flow to the hot table seems to marry up with that test
I did.

why did I decide to move it to the loft.......


Roger wrote:
The message .com
from contains these words:


I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

That is your basic problem.

The vent pipe on the hot outlet means that the run from cold tank to hot
tap is effectively 2 independent parts and if the lower run can pass
water faster than the upper run then air will be drawn in. The pressure
head driving the cold water into the tank can be no more than the
difference in height between the water surface in the cold tank and the
vent junction. The pressure driving the water into the bath is the
height difference between the water level in the vent pipe (maximum when
the level drops to the vent junction) and the bath tap and parity is
reached when the water level in the vent pipe (by then actually in the
hot tap supply pipe) has reduced the head sufficiently for the flows to
match.

You are stuck with the connections you have but every little improvement
will help the flow into the tank. Removing elbows and increasing to 28mm
will both help. There are tables around that will tell you what flow you
should get with various lengths of pipe at various heads and the
equivalent length to add on for each fitting but it seems to me that the
head disparity is so great that you will have to put some restriction in
the feed to the hot tap to avoid drawing in air. A gate valve would do.
Experiment till air is not drawn in and then take off and hide the
handle.

You may be getting the same problem on some or all of your other hot
taps but have not noticed it as full on is less likely on those taps.

One final point. Have you asked yourself does it actually matter if air
is drawn into the hot supply in that manner. I am not entirely sure it
does but it might depend on what is likely to be sucked in with it.

Don't listen to Dribble. He is permanently in my killfile but I couldn't
help noticing he advised you to increase the diameter of the vent pipe.
You won't notice the fraction of a second difference the increased
reservoir in the vent pipe delivers before it starts to feed air.

--
Roger Chapman

FWIW...
There are hw tanks with the cold header tank sat on top of them, and it
can be made to work. Routing the vent pipe thru the header tank would
maintain the ability to blow off expansion but eliminate air sucking.
Whether this is in line with todays regs I dont know though, maybe not.
Having no HW tank vent was how I saw it work, but I'm sure that wouldnt
go down so well today. Whatever you do, if theres any possibility of
hot in the header, the header must be able to handle the heat safely,
as you dont want a blockage to cause a softened plastic header tankful
of boiling water to drop on someone.


NT

Hey-ho, this seems to be a long running thread. Maybe an extra take on
it will help.

1. Are you absolutely sure the cold water feed to the hot tank is
totally unobstructed?

Assuming you had reused components from the old location, or even just
banging stuff about, could have dislodged/moved/introduced an
obstruction.

Assuming you have a gate valve on this pipe, you could disconnect it
and do a "discharge into a bucket" test of flow rate.

2. How about blocking the vent pipe with a hand/thumb over the end
whilst someone else runs the bath tap full blast. This will at least
prove it (or not) as the source of drawn-in air.

wrote in message
ups.com...
wrote:

thanks Roger, appreciate the long detailed response.

just to be clear (as clearly I'm no expert plumber:-) ) the problem is
essentially caused because the head of water between the top of the
cold header and the top of the hot cylinder has not been greatly
reduced because I moved the hot water cylinder in to the loft along
with the cold header.

before I moved the hot cylinder to the loft I had about 6-7 feet head
of water from the top of cold header to the top of the cylinder, and
the head of water to the bath tap would havev been, say, 8-9 feet -
i.e. not much difference.

have I got that all correct?

I did try previously only partially opening the bath hot tap and it did
not seem to have an air in it, so you comment about essentially
restricting the flow to the hot table seems to marry up with that test
I did.

why did I decide to move it to the loft.......


Roger wrote:
The message .com
from contains these words:


I'm running out of ideas and this remains the one obvious difference
to
standard installations that have the cold header in the loft and the
cylinder on the landing

That is your basic problem.

The vent pipe on the hot outlet means that the run from cold tank to
hot
tap is effectively 2 independent parts and if the lower run can pass
water faster than the upper run then air will be drawn in. The pressure
head driving the cold water into the tank can be no more than the
difference in height between the water surface in the cold tank and the
vent junction. The pressure driving the water into the bath is the
height difference between the water level in the vent pipe (maximum
when
the level drops to the vent junction) and the bath tap and parity is
reached when the water level in the vent pipe (by then actually in the
hot tap supply pipe) has reduced the head sufficiently for the flows to
match.

You are stuck with the connections you have but every little
improvement
will help the flow into the tank. Removing elbows and increasing to
28mm
will both help. There are tables around that will tell you what flow
you
should get with various lengths of pipe at various heads and the
equivalent length to add on for each fitting but it seems to me that
the
head disparity is so great that you will have to put some restriction
in
the feed to the hot tap to avoid drawing in air. A gate valve would do.
Experiment till air is not drawn in and then take off and hide the
handle.

You may be getting the same problem on some or all of your other hot
taps but have not noticed it as full on is less likely on those taps.

One final point. Have you asked yourself does it actually matter if air
is drawn into the hot supply in that manner. I am not entirely sure it
does but it might depend on what is likely to be sucked in with it.

Don't listen to Dribble. He is permanently in my killfile but I
couldn't
help noticing he advised you to increase the diameter of the vent pipe.
You won't notice the fraction of a second difference the increased
reservoir in the vent pipe delivers before it starts to feed air.

--
Roger Chapman

FWIW...
There are hw tanks with the cold header
tank sat on top of them, and it
can be made to work.

They come as a prefab unit.

Routing the vent pipe thru the header tank would
maintain the ability to blow off expansion but
eliminate air sucking.

If I understand you this means thee will be a circulation path through the
cold tank. Sp, no.

The cold feed has to be restriction free and a larger bore than open vent.
And the take the open vent back to the tank following the path of the cold
feed,. Do not have the tee to an open vent and draw-off taps at the
cylinder. This also prevents heat rising up the open vent pipe too.

A Surrey flange will work too. Approach is, 28mm cold feed with not
restrictions. If still a problem use a Surrey flange.

"Roger" wrote in message
k...
The message om
from "Dave Liquorice" contains these words:

Ah but is that air actually being sucked in down the vent or is it the
air relased from the water when it is heated?

I am convinced

Roger, be convinced all you like. There are packaged tank cylinder setups
with this sort of head. If what you sad was right they would all suck in
air.