On 2008-01-28 09:35:19 +0000, Fred said:

On Mon, 28 Jan 2008 09:18:52 -0000, "Roger Mills"
wrote:

A by-pass circuit doesn't
protect the pump (most pumps will happily run stalled anyway)

Thanks. On a slightly different note, if pumps will run stalled, what
is the worry about having TRVs closed? I thought if all rads had trvs
then you had to have a bypass to protect the pump?

The pump will become noisier. Generally, TRVs don't close completely
but reduce flow. If the system is set up reasonably, the main room
thermostat will be stopping the CH before that is an issue.



A lot depends on the boiler design. Many modern boilers hold a relatively
small amount of water. When an external control (room stat etc.) turns the
burner off while the boiler is in full flight the residual heat in the metal
parts continues to heat the water - to the extent that it could actually
boil if there is no flow to carry the heat away. Such boilers will only work
with fully pumped systems

You say this heat has to be pumped away; would the convection in a
gravity HW system be insufficient to dissipate this?

That could have been the mechanism before.




I am in the process of trying to find my boiler manufacturer for their
advice.

Particularly, you want to know if a bypass is required when the system
is fully pumped with no gravity and if there is a pump over-run
thermostat

On Mon, 28 Jan 2008 09:47:42 -0000, "Roger Mills"
wrote:

The type of by-pass is important though. Unless there is some mechanism for
keeping the pump running after the boiler demand has been cut, there's no
point in having an automatic bypass because there will never be sufficient
pressure to open it.

Oh. I was going to fit one just to be safe, but now it seems it
wouldn't open (without pump overrun) even if I did!

I cannot find an e-mail address that works for Mistral so I will have
to get in touch by post.

If the boiler can't directly control the pump (it will have specific pump
connection terminals if it can) and if you want to play safe, you could do
the following:
* Fit an automatic by-pass valve in the position discussed above
* Wire the pump to a bathroom fan timer[1] set to (say) 2 minutes.

I used one of hose fan timers for a fan. I set it to 20 minutes; it
ran for seven. The scale is very approximate!

In an earlier contribution to this discussion,
Andy Hall wrote:



I suppose that you could suck it and see with a lockshield valve,
but given the hassle of draining again if it doesn't work, I would put
in an automatic bypass valve and be done with it.


But unless he has some means of over-running the pump [1], an automatic
by-pass will never open.

[1] Either by pump control built into the boiler (unlikely), or using a
timer as I suggested in another post
--
Cheers,
Roger
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In an earlier contribution to this discussion,
Fred wrote:

On Mon, 28 Jan 2008 09:18:52 -0000, "Roger Mills"
wrote:

A by-pass circuit doesn't
protect the pump (most pumps will happily run stalled anyway)

Thanks. On a slightly different note, if pumps will run stalled, what
is the worry about having TRVs closed? I thought if all rads had trvs
then you had to have a bypass to protect the pump?

It's bad practice to have TRVs on *all* rads if that is your only
temperature control because the pump will still run and the boiler will
cycle unnecessarily on its own stat - both of which waste energy. You should
also have a room stat which cuts *everything* off when satisfied - and the
rad in the room containing the room stat mustn't have a TRV, otherwise
there'll be a conflict. A by-pass is primarily to provide a path for the
boiler to dump its heat.

A lot depends on the boiler design. Many modern boilers hold a
relatively small amount of water. When an external control (room
stat etc.) turns the burner off while the boiler is in full flight
the residual heat in the metal parts continues to heat the water -
to the extent that it could actually boil if there is no flow to
carry the heat away. Such boilers will only work with fully pumped
systems

You say this heat has to be pumped away; would the convection in a
gravity HW system be insufficient to dissipate this?


With some boilers, yes. With your particular boiler, obviously not - 'cos
that's how it's been happily operating in the past.
--
Cheers,
Roger
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In an earlier contribution to this discussion,
Fred wrote:

On Mon, 28 Jan 2008 09:47:42 -0000, "Roger Mills"
wrote:


If the boiler can't directly control the pump (it will have specific
pump connection terminals if it can) and if you want to play safe,
you could do the following:
* Fit an automatic by-pass valve in the position discussed above
* Wire the pump to a bathroom fan timer[1] set to (say) 2 minutes.

I used one of hose fan timers for a fan. I set it to 20 minutes; it
ran for seven. The scale is very approximate!

Indeed - but it should operate consistently once set. You can rig it up
temporarily to switch a lamp or somesuch while you're adjusting it.
--
Cheers,
Roger
______
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On 2008-01-28 14:05:40 +0000, "Roger Mills" said:

In an earlier contribution to this discussion,
Andy Hall wrote:



I suppose that you could suck it and see with a lockshield valve,
but given the hassle of draining again if it doesn't work, I would put
in an automatic bypass valve and be done with it.


But unless he has some means of over-running the pump [1], an automatic
by-pass will never open.

[1] Either by pump control built into the boiler (unlikely), or using a
timer as I suggested in another post

Yes I know.

I was looking at it from the perspective of reverse circulation - i.e.
if it doesn't happen with a lockshield valve then no real problem.

OTOH, it might, and it would be less effort to fit an ABV in the first place.

In an earlier contribution to this discussion,
Andy Hall wrote:

On 2008-01-28 14:05:40 +0000, "Roger Mills"
said:

But unless he has some means of over-running the pump [1], an
automatic by-pass will never open.


Yes I know.

I was looking at it from the perspective of reverse circulation - i.e.
if it doesn't happen with a lockshield valve then no real problem.

OTOH, it might, and it would be less effort to fit an ABV in the
first place.

He'd certainly be guaranteed no reverse circulation if the bl**dy thing
never opened! g
--
Cheers,
Roger
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On Mon, 28 Jan 2008 14:13:17 -0000, "Roger Mills"
wrote:

It's bad practice to have TRVs on *all* rads if that is your only
temperature control because the pump will still run and the boiler will
cycle unnecessarily on its own stat - both of which waste energy. You should
also have a room stat which cuts *everything* off when satisfied - and the
rad in the room containing the room stat mustn't have a TRV, otherwise
there'll be a conflict. A by-pass is primarily to provide a path for the
boiler to dump its heat.

There is no TRV on the hall radiator (where the thermostat is) for the
reason you describe, nor is there one in the bathroom. However I
thought I had read here that some people do put them everywhere and
this then causes trouble because the pump has nowhere to push the
water?

I wasn't sure whether to split upstairs and downstairs and make two CH
zones. If there is one rad without a TRv in each, will that be enough?

Thanks.

In an earlier contribution to this discussion,
Fred wrote:

On Mon, 28 Jan 2008 14:13:17 -0000, "Roger Mills"
wrote:

It's bad practice to have TRVs on *all* rads if that is your only
temperature control because the pump will still run and the boiler
will cycle unnecessarily on its own stat - both of which waste
energy. You should also have a room stat which cuts *everything* off
when satisfied - and the rad in the room containing the room stat
mustn't have a TRV, otherwise there'll be a conflict. A by-pass is
primarily to provide a path for the boiler to dump its heat.

There is no TRV on the hall radiator (where the thermostat is) for the
reason you describe, nor is there one in the bathroom. However I
thought I had read here that some people do put them everywhere and
this then causes trouble because the pump has nowhere to push the
water?

I wasn't sure whether to split upstairs and downstairs and make two CH
zones. If there is one rad without a TRv in each, will that be enough?

Thanks.

Enough for what? The pump will be happy enough - and wouldn't really mind if
they all closed - it would just build up a bigger static head of water
(since CH pumps are centrifugal rather than positive displacement types).

If you're asking whether having one rad open per zone will act as a by-pass
(if, indeed, you need one at all) then the answer is NO - 'cos the zone
valves will be closed at the times when a by-pass may be needed.
--
Cheers,
Roger
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On Tue, 29 Jan 2008 07:42:35 GMT, Fred wrote:

I wasn't sure whether to split upstairs and downstairs and make two CH
zones. If there is one rad without a TRv in each, will that be enough?

I have two zones (upstairs and downstairs) with two thermostats (lounge and main
bedroom). The bathroom radiator is on a third loop which is permanently
connected in order to dry towels. Other rooms have thermostatic radiator valves
and we use no other heating under normal circumstances. The upstairs/downstairs
split was done nearly 30 years ago when my wife was working from home in an
upstairs room.

Geo

On Tue, 29 Jan 2008 10:15:23 -0000, "Roger Mills"
wrote:

Enough for what? The pump will be happy enough - and wouldn't really mind if
they all closed - it would just build up a bigger static head of water
(since CH pumps are centrifugal rather than positive displacement types).

This is what I was asking about: the pump. I thought the whole point
of keeping at least one radiator without a TRV was to prevent the pump
from damage.

Have I got that wrong? Is the only reason you do not have TRVs on all
radiators because you need one without by the thermostat?

If the pump does not mind, what is the point of a smart pump; is it
just that a smart pump will be quieter?

Thanks.

On Tue, 29 Jan 2008 16:37:06 GMT, Geo
wrote:

The bathroom radiator is on a third loop which is permanently
connected in order to dry towels.

That's what I have done. The hall rad has no TRV because of the
thermostat and the bath radiator has no TRV to dry the towels. I do
wonder whether I should add a TRV to the bath radiator because surely
once the towels get dry and the room gets warm there's no need for any
more heat?

On Sun, 27 Jan 2008 18:12:26 -0000, "Roger Mills"
wrote:

[about smart pumps]
In simple terms, it's attempting to
produce a more or less constant pressure regardless of flow - although it
can't *quite* achieve that.

Hi,

I was re-reading your post. I just wondered why can't it quite achieve
constant pressure and is there any significance to that?

Thanks again.

Hello again.

I have quoted one of Roger's posts because he explains it better than
I could:

It sounds as if you have separate upstairs and downstairs CH circuits -
probably teeing off near the boiler connections?

Yes.

If that is the case, you
must disconnect the CH flow pipe at the boiler, and blank off the boiler
connection.

That's what I have done.

You can re-use the pipe, but feed it from the *top* end, after
the pump - so that water going to the downstairs rads goes up the 28mm pipe,
through the pump, through the CH zone valve, and back *down* the 22mm pipe
(i.e. the opposite way to before) to the downstairs rads.

I have done this, so that what used to carry hot water to the upstairs
radiators now carries hot water in the opposite direction to the
downstairs radiators.

I was thinking that previously the downstairs radiators were nearest
the boiler but now that they are at the other end of this pipe, they
have moved further away. Does this mean that I need to re balance the
system? Is there a danger that the upstairs radiators now being on a
shorter pipe run will "steal" all the water from the downstairs rads?

I would like to keep the upstairs and downstairs rads on separate
circuits. We discussed fitting a gate valve to the HW circuit to
throttle that from stealing the CH water. I presume no gate valve is
needed to balance upstairs versus downstairs CH since this could all
be done at the lockshields?

Thanks.

On Sun, 27 Jan 2008 17:05:57 +0000, Andy Hall
wrote:

Previously, the vent pipe and the feed/expansion pipe were effectively
connected at two points on the gravity circuit with the cylinder.
The flow rate and hence the pressure between the two will have been
very low and not enough to cause pumping over from the vent pipe or
sucking down through the feed pipe.

Now you are putting the resistance of part of the boiler heat
exchanger, a run of pipe and possibly the pump between the two.
There will be a much stronger flow because of the pump and there will
be a pressure difference between the two places on the circuit where
the vent and the feed pipe are connected. That may be enough to
cause the aforesaidmentioned pumping over or sucking down. You don't
want that because apart from the noise and the water vapour and heat
loss in the loft, it will accelerate corrosion of the system because of
introduced oxygen.

I have moved the pump from the kitchen to the airing cupboard. As long
as it does not keep me awake, that's where it will stay. When the pump
was downstairs there was a lot of water above it. Now that it's
upstairs there is less water above it, so do I need to be more
concerned about sucking air down through the vent pipe? I'm wondering
whether it would be easier for the pump to suck air through the
relatively short vent pipe rather than suck water up from much longer
the downstairs CH circuit?

I have connected 2-port valves set in manual override (I'm about to
wire them; please see my other post). Last night the upstairs rads got
hot but the downstairs ones were stone cold. I wondered whether this
could be a factor?

The other thing is, the pipe work to the airing cupboard will be the
highest point of the downstairs circuit, so do I need to add a bleed
valve somewhere to let air out?

The strange thing is that this morning, the downstairs rads were
beginning to heat, so I can't understand why yesterday they did not
work and today they are! Any ideas what's going on?

Some of my rads are fitted with Aladdin automatic bleed valves from
toolstation. For some reason when I refilled the CH these did not
bleed and the manual override did not work either. I was very
disappointed and had to manually bleed the rads with a spanner. Are
these automatic valves a waste of time?

Thanks.

On Sun, 27 Jan 2008 17:05:57 +0000, Andy Hall
wrote:

The alternative, is an air separator. Have a look at www.bes.ltd.uk
product code 11334 or 11335. To use one of these, you would insert it
on the flow from the boiler before the pump and then connect both the
FE pipe and the vent pipe to it.

I have had a look at this and also the model for sale at Toolstation
(order code 75473). The toolstation one has one fewer connections;
why?

In an earlier contribution to this discussion,
Fred wrote:

On Tue, 29 Jan 2008 10:15:23 -0000, "Roger Mills"
wrote:

Enough for what? The pump will be happy enough - and wouldn't really
mind if they all closed - it would just build up a bigger static
head of water (since CH pumps are centrifugal rather than positive
displacement types).

This is what I was asking about: the pump. I thought the whole point
of keeping at least one radiator without a TRV was to prevent the pump
from damage.

Have I got that wrong? Is the only reason you do not have TRVs on all
radiators because you need one without by the thermostat?

If the pump does not mind, what is the point of a smart pump; is it
just that a smart pump will be quieter?

Thanks.

Yes, that - plus the fact that it will use less electricity when it
throttles back.
--
Cheers,
Roger
______
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PLEASE REPLY TO NEWSGROUP!

In an earlier contribution to this discussion,
Fred wrote:

On Sun, 27 Jan 2008 18:12:26 -0000, "Roger Mills"
wrote:

[about smart pumps]
In simple terms, it's attempting to
produce a more or less constant pressure regardless of flow -
although it can't *quite* achieve that.

Hi,

I was re-reading your post. I just wondered why can't it quite achieve
constant pressure and is there any significance to that?

Thanks again.

If you look at the performance curves for a non-smart pump would will see
that there are three (for a 3-speed pump) curved lines - each showing
pressure vs flow for one of the speeds. Pressure is on the vertical axis,
and flow on the horizontal axis. Each curve slopes downwards to the right,
with a high pressure at zero flow and a high flow at zero pressure.

A smart pump, instead of running at one of the manually selected speeds,
will automatically vary the speed according to the flow resistance it
detects. But its range is speeds is limited to somewhere between the highest
and lowest fixed speeds of its manual cousin - rather than being infinite.
So, for example, once it's dropped to its lowest speed, if further
restriction is imposed by (say) more TRVs closing, the pressure will start
to rise and there's nothing it can do about it.

So, in summary, it varies its speed in order to *try* to produce a more or
less constant pressure but outside its range of control it simply follows
the pressure vs flow curves like an 'ordinary' pump.
--
Cheers,
Roger
______
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On Thu, 31 Jan 2008 09:40:57 -0000, "Roger Mills"
wrote:

So, in summary, it varies its speed in order to *try* to produce a more or
less constant pressure but outside its range of control it simply follows
the pressure vs flow curves like an 'ordinary' pump.

Thank you.

In an earlier contribution to this discussion,
Fred wrote:

Hello again.

I have quoted one of Roger's posts because he explains it better than
I could:

It sounds as if you have separate upstairs and downstairs CH
circuits - probably teeing off near the boiler connections?

Yes.

If that is the case, you
must disconnect the CH flow pipe at the boiler, and blank off the
boiler connection.

That's what I have done.

You can re-use the pipe, but feed it from the *top* end, after
the pump - so that water going to the downstairs rads goes up the
28mm pipe, through the pump, through the CH zone valve, and back
*down* the 22mm pipe (i.e. the opposite way to before) to the
downstairs rads.

I have done this, so that what used to carry hot water to the upstairs
radiators now carries hot water in the opposite direction to the
downstairs radiators.

I was thinking that previously the downstairs radiators were nearest
the boiler but now that they are at the other end of this pipe, they
have moved further away. Does this mean that I need to re balance the
system? Is there a danger that the upstairs radiators now being on a
shorter pipe run will "steal" all the water from the downstairs rads?

I would like to keep the upstairs and downstairs rads on separate
circuits. We discussed fitting a gate valve to the HW circuit to
throttle that from stealing the CH water. I presume no gate valve is
needed to balance upstairs versus downstairs CH since this could all
be done at the lockshields?

Thanks.

It's quite likely that the balance will have been upset by the significant
changes which you have made to the system.

I would balance the *whole* CH system - with both heating zones on and HW
off, just by adjusting the lockshields - no additional gate valves needed.
The, when you're only running *one* heating zone, the individual rads within
that zone should remain reasonably in balance.

As far as balancing CH vs HW, its a suck it and see job. As I said earlier,
if you can arrange the timing so that CH and HW are not usually on at the
same time, so much the better. Otherwise start with the HW gate valve fully
open and see if you notice any adverse effects on the heating when the HW is
on. If so, throttle the HW back a bit and try to find a position where it
still gets hot quickly enough without affecting the CH. I don't think
there's a scientific way of doing it (like balancing radiators) because you
never have steady state conditions when heating the HW.
--
Cheers,
Roger
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On Thu, 31 Jan 2008 08:27:44 GMT someone who may be Fred
wrote this:-

That's what I have done. The hall rad has no TRV because of the
thermostat and the bath radiator has no TRV to dry the towels. I do
wonder whether I should add a TRV to the bath radiator because surely
once the towels get dry and the room gets warm there's no need for any
more heat?

The ideal option is to have a radiator in the bathroom to warm the
room. This should be fitted with a TRV.

To dry the towels a towel rail should be fitted. This is best not
connected to the heating circuit as it will then not be on in the
summer (unless it is fitted with an electric element). It can be fed
from either the primary or secondary side of the hot water system.
There are advantages in feeding it by gravity from the secondary
side.

If the towel rail manages to warm the room up enough, as it is
likely to do in spring and autumn, the TRV will prevent the radiator
coming on.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In an earlier contribution to this discussion,
Fred wrote:


I have moved the pump from the kitchen to the airing cupboard. As long
as it does not keep me awake, that's where it will stay. When the pump
was downstairs there was a lot of water above it. Now that it's
upstairs there is less water above it, so do I need to be more
concerned about sucking air down through the vent pipe? I'm wondering
whether it would be easier for the pump to suck air through the
relatively short vent pipe rather than suck water up from much longer
the downstairs CH circuit?

The pump doesn't have to *suck* water up from downstairs - it simply has to
*circulate* the water in the system. Some of the water which it circulates
flows downstairs and pushes the downstairs water up. The pump can only work
when the system is full of water, and all the air bled out in order to
provide a continuous water circuit.


I have connected 2-port valves set in manual override (I'm about to
wire them; please see my other post). Last night the upstairs rads got
hot but the downstairs ones were stone cold. I wondered whether this
could be a factor?

Chances are that you had an airlock in the downstairs circuit, preventing
circulation.

The other thing is, the pipe work to the airing cupboard will be the
highest point of the downstairs circuit, so do I need to add a bleed
valve somewhere to let air out?

That would be a good idea - and would also make sure that there's no air in
or near the pump.

The strange thing is that this morning, the downstairs rads were
beginning to heat, so I can't understand why yesterday they did not
work and today they are! Any ideas what's going on?

Sounds like the air-lock has moved, and the air settled out somewhere -
probably in a radiator.

Some of my rads are fitted with Aladdin automatic bleed valves from
toolstation. For some reason when I refilled the CH these did not
bleed and the manual override did not work either. I was very
disappointed and had to manually bleed the rads with a spanner. Are
these automatic valves a waste of time?


Dunno - never used them!
--
Cheers,
Roger
______
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On Thu, 31 Jan 2008 09:40:57 -0000 someone who may be "Roger Mills"
wrote this:-

A smart pump, instead of running at one of the manually selected speeds,
will automatically vary the speed according to the flow resistance it
detects. But its range is speeds is limited to somewhere between the highest
and lowest fixed speeds of its manual cousin - rather than being infinite.

To add to this. It may be possible to run a pump at down to about
50% of its minimum manual speed, with a sufficiently good controller
which produces a good waveform. Less good controllers tend to
shorten pump life. Going any lower is likely to damage the pump.

In theory the speed could be reduced to zero, but this would require
a rather more expensive controller and pump than is typical in
domestic heating systems as it would involve three phase motors fed
by an inverter from the single phase supply.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Thu, 31 Jan 2008 11:11:52 -0000, "Roger Mills"
wrote:

The other thing is, the pipe work to the airing cupboard will be the
highest point of the downstairs circuit, so do I need to add a bleed
valve somewhere to let air out?

That would be a good idea - and would also make sure that there's no air in
or near the pump.

Thanks. I presume I insert a tee with something in the top; what is
the something in the top? Do I use a drain cock or do I use a 15mm to
1/2 inch adaptor and screw in a radiator bleed valve, or is there a
special fitting just for the job, of which I am currently unaware?

Thanks,

On 2008-01-31 09:05:11 +0000, Fred said:

On Sun, 27 Jan 2008 17:05:57 +0000, Andy Hall
wrote:

The alternative, is an air separator. Have a look at www.bes.ltd.uk
product code 11334 or 11335. To use one of these, you would insert it
on the flow from the boiler before the pump and then connect both the
FE pipe and the vent pipe to it.

I have had a look at this and also the model for sale at Toolstation
(order code 75473). The toolstation one has one fewer connections;
why?

That one only has circuit in and out and vent.

It will address the issue of separating out circulating air, but not
the risk of pumping over/sucking down. You would have to make sure
that the feed is connected close to it to do that. Given that
situation, you might as well get the four connection version and solve
the entire (risk of a) problem in one go

On Fri, 1 Feb 2008 08:06:57 +0000, Andy Hall
wrote:

That one only has circuit in and out and vent.

It will address the issue of separating out circulating air, but not
the risk of pumping over/sucking down. You would have to make sure
that the feed is connected close to it to do that. Given that
situation, you might as well get the four connection version and solve
the entire (risk of a) problem in one go

Thanks for the explanation. I understand now. Because I picked the
wrong time of year to do this, I have had the CH on and without the
separator there have been no problems yet, other than the downstairs
rads not getting warm quickly which I think is because the system is
now unbalanced.

In an earlier contribution to this discussion,
Fred wrote:

On Thu, 31 Jan 2008 11:11:52 -0000, "Roger Mills"
wrote:

The other thing is, the pipe work to the airing cupboard will be the
highest point of the downstairs circuit, so do I need to add a bleed
valve somewhere to let air out?

That would be a good idea - and would also make sure that there's no
air in or near the pump.

Thanks. I presume I insert a tee with something in the top; what is
the something in the top? Do I use a drain cock or do I use a 15mm to
1/2 inch adaptor and screw in a radiator bleed valve, or is there a
special fitting just for the job, of which I am currently unaware?

Thanks,

There are special fittings. I can't give you a direct URL, but go to
http://www.bes.co.uk/ , search for Air Vent, then take the first option and
scroll down to parts 6793 and 9178 - which solder onto the end of a 15mm or
22mm pipe respectively, or 16383 which mounts in a 15mm compression fitting.
Or any of the others which might take your fancy!
--
Cheers,
Roger
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On Fri, 1 Feb 2008 11:56:53 -0000, "Roger Mills"
wrote:

http://www.bes.co.uk/
[snip]
16383 which mounts in a 15mm compression fitting.


That sounds good as I'm not well practiced at soldering yet. The
problem with BES is that the postage is quite high, so I need to find
a few more things to order to justify the postage charge.

In an earlier contribution to this discussion,
Fred wrote:

On Fri, 1 Feb 2008 11:56:53 -0000, "Roger Mills"
wrote:

http://www.bes.co.uk/
[snip]
16383 which mounts in a 15mm compression fitting.


That sounds good as I'm not well practiced at soldering yet. The
problem with BES is that the postage is quite high, so I need to find
a few more things to order to justify the postage charge.


Or try to find something similar at a local plumbers merchant.
--
Cheers,
Roger
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