I posted this thread a few weeks ago
(http://groups.google.com/group/uk.d-...b3b8b37b5b6866)
complaining of problems with air being sucked down the vent/expansion
pipe when I moved my cylinder to the loft and thus lost the substantial
head of water between tank and cylinder.

Most recommended upgrading the pipe from the tank to the cylinder,
which I did to a healthy 28mm copper. It worked a treat. Many, many
baths later and no air was being sucked in.

And then....it all went wrong again. Every time I open the hot bath tap
air is getting regularly sucked in the vent pipe again. What has
changed, what I have done - nothing!

So first thought was, it must be a blockage in the 28mm pipe, hard to
check but I'm fairly certain its not that because - well - what could
block it?

So my second thought was, I lied earlier as I have actually 'changed'
something. And that is that I've now hooked up my boiler and it (the
boiler) is able to heat the water in the cylinder via the coil. (Before
I was using the immersion, very expensive - ouch!).

And there we are, am I going mad? Did it ever work when I changed it to
28mm - or was it just a dream? The ONLY thing that has change is that
the hot water is now heated by the coil - is there ANY WAY that this
could be a source of a problem?

On Mon, 09 Oct 2006 09:16:46 -0700, grahamrichardnorth wrote:

Is there any significant difference in the temperature that the immersion
and the boiler heat the cylinder to?

Is the temperature when connected to the boiler controlled by a cylinder
thermostat or just the boiler's stat?



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

yes there is a difference, the immersion was set very high (because of
the problems I had getting any water out in the early stages) at about
75/80, whereas now its about 65 degrees C

Sirett wrote:
On Mon, 09 Oct 2006 09:16:46 -0700, grahamrichardnorth wrote:

Is there any significant difference in the temperature that the immersion
and the boiler heat the cylinder to?

Is the temperature when connected to the boiler controlled by a cylinder
thermostat or just the boiler's stat?



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

sorry, and yes it has a cylinder stat controlling this. it doesn't rely
on the boiler stat

wrote:
yes there is a difference, the immersion was set very high (because of
the problems I had getting any water out in the early stages) at about
75/80, whereas now its about 65 degrees C

Sirett wrote:
On Mon, 09 Oct 2006 09:16:46 -0700, grahamrichardnorth wrote:

Is there any significant difference in the temperature that the immersion
and the boiler heat the cylinder to?

Is the temperature when connected to the boiler controlled by a cylinder
thermostat or just the boiler's stat?



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

wrote in message
ps.com...
I posted this thread a few weeks ago

(http://groups.google.com/group/uk.d-...cabb52bcd8fba/
bbb3b8b37b5b6866?lnk=st&rnum=1#bbb3b8b37b5b6866)
complaining of problems with air being sucked down the vent/expansion
pipe when I moved my cylinder to the loft and thus lost the substantial
head of water between tank and cylinder.

Most recommended upgrading the pipe from the tank to the cylinder,
which I did to a healthy 28mm copper. It worked a treat. Many, many
baths later and no air was being sucked in.

And then....it all went wrong again. Every time I open the hot bath tap
air is getting regularly sucked in the vent pipe again. What has
changed, what I have done - nothing!

So first thought was, it must be a blockage in the 28mm pipe, hard to
check but I'm fairly certain its not that because - well - what could
block it?

So my second thought was, I lied earlier as I have actually 'changed'
something. And that is that I've now hooked up my boiler and it (the
boiler) is able to heat the water in the cylinder via the coil. (Before
I was using the immersion, very expensive - ouch!).

And there we are, am I going mad? Did it ever work when I changed it to
28mm - or was it just a dream? The ONLY thing that has change is that
the hot water is now heated by the coil - is there ANY WAY that this
could be a source of a problem?


I've just sketched your system. I think this would explain it:

The water level in the vent pipe will be the same as in the tank. The
junction where the hot water Ts off from the vent pipe is not much below the
water level when the tank is full. When you run a bath, the level in the
tank drops, as does the level in the vent pipe, until it reaches the T, when
air stars to get drawn in.

The reason it was less of a problem with the immersion heater was that the
water was hotter, so you used less of it. The level didn't drop enough to
cause a problem.

To prevent this happening you need the T to be below the lowest tank level
possible, so raise the tank more, fit a shorter, fatter cylinder or move it
back downstairs. Depending on the height of the T you may be able to
re-plumb it nearer to the top of the cylinder, which could be the easiest
solution.

HTH

Mark

Thanks for your response, but I'm not sure I agree with your
explanation, probably because I've not explained enough about the
system and therefore you don't have the full details.

Air gets sucked in immediately when I turn on the hot tap, it doesn't
get sucked in when the water in the tank has dropped to a certain
level. Before I changed to 28mm I could understand why a sudden gush of
water to the hot tap could suck some water out of the vent pipe as well
as the cylinder, but with 28mm feeding the cylinder (and that 28mm is
copper) and 22mm plastic pipe (with inserts too) exiting the cylinder I
couldn't see how, even with the difference in the head of height, the
22mm could be sucking more than the 28mm could be supplying.

I've also extended the vent pipe horizontally to compensate (slightly)
for the much smaller head of water. I now have at least 6 feet of water
in the 22mm vent pipe, albeit horizonally (slightly sloping upwards
always) rather than purely vertically as normal.

This system HAS been working, when I changed to 28mm I tested and
tested to make sure that the problem had gone away. The fact that it
has come back either means that something is blocking the 28mm pipe
from the tank to the cylinder, or that the change in heating device has
effected it somehow. I can't think of anything else that could cause
this.

I've noticed that since changing to heating via the coil the bottom
brass connection to the cylinder (the one from the tank) now feels
quite warm. I assume because the coil reaches much lower than any
immersion element could. But could this cause a problem, could the
difference in water temperature cause unwanted turbulence in the water
when the cold water comes in to the bottom of the cylinder from the
tank, and could this mean that I'm back to square one?

You'll notice that I don't really have a clue why this is happening and
am starting to make up reasons ;-)

MarkK wrote:
wrote in message
ps.com...
I posted this thread a few weeks ago

(http://groups.google.com/group/uk.d-...cabb52bcd8fba/
bbb3b8b37b5b6866?lnk=st&rnum=1#bbb3b8b37b5b6866)
complaining of problems with air being sucked down the vent/expansion
pipe when I moved my cylinder to the loft and thus lost the substantial
head of water between tank and cylinder.

Most recommended upgrading the pipe from the tank to the cylinder,
which I did to a healthy 28mm copper. It worked a treat. Many, many
baths later and no air was being sucked in.

And then....it all went wrong again. Every time I open the hot bath tap
air is getting regularly sucked in the vent pipe again. What has
changed, what I have done - nothing!

So first thought was, it must be a blockage in the 28mm pipe, hard to
check but I'm fairly certain its not that because - well - what could
block it?

So my second thought was, I lied earlier as I have actually 'changed'
something. And that is that I've now hooked up my boiler and it (the
boiler) is able to heat the water in the cylinder via the coil. (Before
I was using the immersion, very expensive - ouch!).

And there we are, am I going mad? Did it ever work when I changed it to
28mm - or was it just a dream? The ONLY thing that has change is that
the hot water is now heated by the coil - is there ANY WAY that this
could be a source of a problem?


I've just sketched your system. I think this would explain it:

The water level in the vent pipe will be the same as in the tank. The
junction where the hot water Ts off from the vent pipe is not much below the
water level when the tank is full. When you run a bath, the level in the
tank drops, as does the level in the vent pipe, until it reaches the T, when
air stars to get drawn in.

The reason it was less of a problem with the immersion heater was that the
water was hotter, so you used less of it. The level didn't drop enough to
cause a problem.

To prevent this happening you need the T to be below the lowest tank level
possible, so raise the tank more, fit a shorter, fatter cylinder or move it
back downstairs. Depending on the height of the T you may be able to
re-plumb it nearer to the top of the cylinder, which could be the easiest
solution.

HTH

Mark

wrote in message
ps.com...
I posted this thread a few weeks ago
(http://groups.google.com/group/uk.d-...b3b8b37b5b6866)
complaining of problems with air being sucked down the vent/expansion
pipe when I moved my cylinder to the loft and thus lost the substantial
head of water between tank and cylinder.

Most recommended upgrading the pipe from the tank to the cylinder,
which I did to a healthy 28mm copper. It worked a treat. Many, many
baths later and no air was being sucked in.

And then....it all went wrong again. Every time I open the hot bath tap
air is getting regularly sucked in the vent pipe again. What has
changed, what I have done - nothing!

So first thought was, it must be a blockage in the 28mm pipe, hard to
check but I'm fairly certain its not that because - well - what could
block it?

So my second thought was, I lied earlier as I have actually 'changed'
something. And that is that I've now hooked up my boiler and it (the
boiler) is able to heat the water in the cylinder via the coil. (Before
I was using the immersion, very expensive - ouch!).

And there we are, am I going mad? Did it ever work when I changed it to
28mm - or was it just a dream? The ONLY thing that has change is that
the hot water is now heated by the coil - is there ANY WAY that this
could be a source of a problem?

Is the cold header tank clean?

Just wondering if there is some crud getting sucked onto the outlet that is
connected to the hot water cylinder - when you upgraded it, it may have
shifted, but has now found it's way back to the outlet, and is partially
blocking it?

Did you change the outlet when you upped to pipe size?

Sparks...

wrote in message
ups.com...
Thanks for your response, but I'm not sure I agree with your
explanation, probably because I've not explained enough about the
system and therefore you don't have the full details.


So how much below the lowest possible water level in the tank is the T? It's
vertical separation that counts. How much below the full level too?

I've also extended the vent pipe horizontally to compensate (slightly)
for the much smaller head of water. I now have at least 6 feet of water
in the 22mm vent pipe, albeit horizonally (slightly sloping upwards
always) rather than purely vertically as normal.

According to the textbooks the "top" of the T should be at 45 degrees, the
"upright" at 45 degrees pointing downwards, such that any bubbles escape up
the vent without entering the hot water feed. I think you've been told this
before.

The original system in my house had a vertical "top" to the T and a
horizontal hot water feed. Bubbles got into it and we used to get air in the
hot water just like you. When I re-plumbed the house I did it as per the
text books and haven't had any air in the water since.

By making the vent close to horizontal you've made a trap for all the
bubbles generated by the heating coil. These are being drawn in and hence
you get air mixed straight away. Maybe.

Plus there isn't enough vertical head, so after the bubbles are drawn in the
effect of insufficient head comes into play, as Roger described in the
previous thread. Again, maybe.

Post an accurate scale diagram somewhere for us and I'm sure someone will
come up with the answer (though I suspect there are at least 2 issues, and
that they have both been covered).

Mark

I'll post some pictures tonight, and label the appropriate parts (even
experienced plumbers may not be able to determine what everything is in
my setup ;-) )


Sparks wrote:
wrote in message
ps.com...
I posted this thread a few weeks ago
(http://groups.google.com/group/uk.d-...b3b8b37b5b6866)
complaining of problems with air being sucked down the vent/expansion
pipe when I moved my cylinder to the loft and thus lost the substantial
head of water between tank and cylinder.

Most recommended upgrading the pipe from the tank to the cylinder,
which I did to a healthy 28mm copper. It worked a treat. Many, many
baths later and no air was being sucked in.

And then....it all went wrong again. Every time I open the hot bath tap
air is getting regularly sucked in the vent pipe again. What has
changed, what I have done - nothing!

So first thought was, it must be a blockage in the 28mm pipe, hard to
check but I'm fairly certain its not that because - well - what could
block it?

So my second thought was, I lied earlier as I have actually 'changed'
something. And that is that I've now hooked up my boiler and it (the
boiler) is able to heat the water in the cylinder via the coil. (Before
I was using the immersion, very expensive - ouch!).

And there we are, am I going mad? Did it ever work when I changed it to
28mm - or was it just a dream? The ONLY thing that has change is that
the hot water is now heated by the coil - is there ANY WAY that this
could be a source of a problem?

Is the cold header tank clean?

Just wondering if there is some crud getting sucked onto the outlet that is
connected to the hot water cylinder - when you upgraded it, it may have
shifted, but has now found it's way back to the outlet, and is partially
blocking it?

Did you change the outlet when you upped to pipe size?

Sparks...

yes there is a difference, the immersion was set very high (because of
the problems I had getting any water out in the early stages) at about
75/80, whereas now its about 65 degrees C

That might be the difference. Because the water is now cooler, it needs more
hot to cold. If you are using a mixer tap, this might result in a greater
hot water flow, if the limitation to the flow rate is the mixer spout.

Christian.

So....after what has seemed like years, the hot water flow is FINALLY
fixed!!

THE CAUSE? a plastic cut-out disc from the cold water storage tank that
I hadn't removed after drilling out one of the tank connector holes

HOW I DISCOVERED THIS? well I was installing a Surrey flange at the top
of the hot water cylinder, and after removing the existing fitting I
notice something bobbing up and down at the top of the cylinder - after
fishing it out I discovered the cut-out from the recently installed
cold water storage tank

AND HOW IS THE HOT WATER FLOW NOW? well the water is perfect! power
shower works fine whilst all other taps are on in the house. this may
have something to do with the new Surrey flange, but that damn plastic
disc is (I'm convinced) the source of most of the problems!

HOW ANNOYED WAS I ? very ;-)

it was as simple as that!

cheers to all who showed an interest, Graham



wrote:
I posted this thread a few weeks ago
(http://groups.google.com/group/uk.d-...b3b8b37b5b6866)
complaining of problems with air being sucked down the vent/expansion
pipe when I moved my cylinder to the loft and thus lost the substantial
head of water between tank and cylinder.

Most recommended upgrading the pipe from the tank to the cylinder,
which I did to a healthy 28mm copper. It worked a treat. Many, many
baths later and no air was being sucked in.

And then....it all went wrong again. Every time I open the hot bath tap
air is getting regularly sucked in the vent pipe again. What has
changed, what I have done - nothing!

So first thought was, it must be a blockage in the 28mm pipe, hard to
check but I'm fairly certain its not that because - well - what could
block it?

So my second thought was, I lied earlier as I have actually 'changed'
something. And that is that I've now hooked up my boiler and it (the
boiler) is able to heat the water in the cylinder via the coil. (Before
I was using the immersion, very expensive - ouch!).

And there we are, am I going mad? Did it ever work when I changed it to
28mm - or was it just a dream? The ONLY thing that has change is that
the hot water is now heated by the coil - is there ANY WAY that this
could be a source of a problem?