Hi,

I'm halfway through converting my gravity HW into a pumped solution.

One thing that puzzles me: when the HW is on the water will be pumped
through 22mm to the cylinder. When the CH is on, water will be pumped
through 15mm to the radiators. Won't there be less resistance in the
HW circuit and if so, how do I throttle the HW so that it doesn't take
all the heat from the CH?

Can I heat the cylinder with the immersion heater whilst the CH is
drained or will that damage the cylinder?

Thanks in advance.

On Sat, 26 Jan 2008 20:16:01 GMT, Fred wrote:

One thing that puzzles me: when the HW is on the water will be pumped
through 22mm to the cylinder. When the CH is on, water will be pumped
through 15mm to the radiators. Won't there be less resistance in the
HW circuit and if so, how do I throttle the HW so that it doesn't take
all the heat from the CH?

The three port valve will only route water through the cylinder coil when
the cyclinder stat is calling for heat. Most people will require the HW to
recover as quickly as possible and the short time (30 mins/hour) that it
takes for the cylinder to recover from *completely* cold won't have a
particulary noticeable effect on the CH, which will still have some flow.

Can I heat the cylinder with the immersion heater whilst the CH is
drained or will that damage the cylinder?

Should be fine.

--
Cheers
Dave. pam is missing e-mail

In an earlier contribution to this discussion,
Fred wrote:

Hi,

I'm halfway through converting my gravity HW into a pumped solution.

One thing that puzzles me: when the HW is on the water will be pumped
through 22mm to the cylinder. When the CH is on, water will be pumped
through 15mm to the radiators. Won't there be less resistance in the
HW circuit and if so, how do I throttle the HW so that it doesn't take
all the heat from the CH?

Have you currently got 4 pipes connected to the boiler - 2 for the (gravity)
HW, and 2 for the (pumped) CH? If so, exactly how are you re-arranging it?
One or 2 pumps in total? How many/what sort of motorised valves? Where?

Can I heat the cylinder with the immersion heater whilst the CH is
drained or will that damage the cylinder?


You can do that - the cylinder will be fine.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sat, 26 Jan 2008 20:16:01 GMT, Fred
wrote:

Hi,

I'm halfway through converting my gravity HW into a pumped solution.

One thing that puzzles me: when the HW is on the water will be pumped
through 22mm to the cylinder. When the CH is on, water will be pumped
through 15mm to the radiators. Won't there be less resistance in the
HW circuit and if so, how do I throttle the HW so that it doesn't take
all the heat from the CH?

Can I heat the cylinder with the immersion heater whilst the CH is
drained or will that damage the cylinder?

Thanks in advance.

The Domestic HW and the Heating water are kept seperate from each
other ,the domestic HW in the cylinder being heated by a pipe that
runs round the cylinder and heats the water which then gets taken to
the taps from the top of the cylinder and refilled at the foot of the
cylinder by a cold water feed.

The immersion heater heats the water that is in the cylinder and there
is no reason that I know why you cannot have it switched on so long as
there continues to be a supply of water to the cylinder .

Why are you converting it anyway ?

On Sat, 26 Jan 2008 22:34:44 -0000, "Roger Mills"
wrote:

Have you currently got 4 pipes connected to the boiler - 2 for the (gravity)
HW, and 2 for the (pumped) CH? If so, exactly how are you re-arranging it?
One or 2 pumps in total? How many/what sort of motorised valves? Where?

I am moving the pump from by the boiler to the airing cupboard based
on advice posted, I think by yourself, in this group.

The pump used to be on the CH return. Now it will be on the feed,
after the vent to keep that clear, and after the pump will be 2-port
valve for HW and a 2-port valve for CH.

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

Thanks to everyone who posted about the immersion. I thought it would
be ok but wanted to check the heat exchanger or whatever it is called
would not be damaged by being surrounded with hot water whilst empty.
OTOH I think it's just a 22mm coil, so I should have realised it would
be ok to be immersed in 60C water.

Thanks again.

On 2008-01-27 08:14:56 +0000, Fred said:

On Sat, 26 Jan 2008 22:34:44 -0000, "Roger Mills"
wrote:

Have you currently got 4 pipes connected to the boiler - 2 for the (gravity)
HW, and 2 for the (pumped) CH? If so, exactly how are you re-arranging it?
One or 2 pumps in total? How many/what sort of motorised valves? Where?

I am moving the pump from by the boiler to the airing cupboard based
on advice posted, I think by yourself, in this group.

The pump used to be on the CH return. Now it will be on the feed,
after the vent to keep that clear, and after the pump will be 2-port
valve for HW and a 2-port valve for CH.

It's also important to make sure that the feed/expansion pipe and the
vent pipe are not on opposite sides of the pump or even opposite sides
of the boiler. If they are on a pipe run, then no more than 150mm
apart. Even better connect to an air separator such as a Myson Aerjec.
In any case there needs to be a clear path from the boiler to the vent.





Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?


Yes, but they should join at a common point. There shouldn't be any
other branches such as radiator returns between there and the boiler.

In an earlier contribution to this discussion,
Fred wrote:

On Sat, 26 Jan 2008 22:34:44 -0000, "Roger Mills"
wrote:

Have you currently got 4 pipes connected to the boiler - 2 for the
(gravity) HW, and 2 for the (pumped) CH? If so, exactly how are you
re-arranging it? One or 2 pumps in total? How many/what sort of
motorised valves? Where?

I am moving the pump from by the boiler to the airing cupboard based
on advice posted, I think by yourself, in this group.


I may well have done. There are often threads like this, and one tends to
lose track. g


The pump used to be on the CH return. Now it will be on the feed,
after the vent to keep that clear, and after the pump will be 2-port
valve for HW and a 2-port valve for CH.

So you'll have just one pair of boiler connections, with the pipes between
the boiler and airing cupboard being shared by both circuits? If you are
contemplating having both circuits running at the same time, there is a
*possibility* that the HW circuit may hog all the flow and starve the CH
circuit - it's really a suck-it-and-see job. As a precaution, you could fit
a gate valve on the outlet side of the HW coil, which could if necessary be
turned down to balance the HW vs CH flow. Another - probably better -
solution is to try to contrive that both will *not* normally be running at
the same time. If you fit a programmable stat to the CH, you can use the
main programmer to time just the HW - and arrange for that to come on (say)
an hour before the CH so that the HW demand is satisfied before the CH
starts.

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

They can be combined, and this is usual in a fully-pumped system. The
important thing to make sure of is that *all* of the radiator returns are
combined into a single pipe before it joins into the HW return. Otherwise
you may get odd things - such as reverse circulation - occurring under some
circumstances.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sun, 27 Jan 2008 08:43:38 +0000, Andy Hall
wrote:

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

Yes, but they should join at a common point. There shouldn't be any
other branches such as radiator returns between there and the boiler.

No there aren't (what would happen if there were?)

I have two 15mm rad returns, one 22mm hw return and 22mm to the
boiler, so I'm going to need a couple of 22-15-22 or 22-22-15 tees.
Does it matter which?

Thanks.

In an earlier contribution to this discussion,
Fred wrote:

On Sun, 27 Jan 2008 08:43:38 +0000, Andy Hall
wrote:

Can I join the HW and CH return into one 22m pipe or should they
have separate returns to the boiler?

Yes, but they should join at a common point. There shouldn't be any
other branches such as radiator returns between there and the boiler.

No there aren't (what would happen if there were?)


See my previous post.


I have two 15mm rad returns, one 22mm hw return and 22mm to the
boiler, so I'm going to need a couple of 22-15-22 or 22-22-15 tees.
Does it matter which?

Thanks.

Surely that's determined by the pipe layout - i.e. whether or not the 22mm
pipe turns through a right angle at the connection point. Actually, I think
I might be tempted to use 22x22x22 tees plus 22x15 reducers a little way
along the CH pipes.

--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sun, 27 Jan 2008 11:48:31 -0000, "Roger Mills"
wrote:

So you'll have just one pair of boiler connections, with the pipes between
the boiler and airing cupboard being shared by both circuits?

Yes.

If you are
contemplating having both circuits running at the same time, there is a
*possibility* that the HW circuit may hog all the flow and starve the CH

That's what had worried me.

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

They can be combined, and this is usual in a fully-pumped system. The
important thing to make sure of is that *all* of the radiator returns are
combined into a single pipe before it joins into the HW return.

Can I have two rad returns join the HW return in a tee or should I tee
the two rad returns together first?

Otherwise you may get odd things - such as reverse circulation - occurring under some
circumstances.

Out of interest, what circumstances would cause that?

Thanks.

On 2008-01-27 12:08:48 +0000, Fred said:

On Sun, 27 Jan 2008 08:43:38 +0000, Andy Hall
wrote:

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

Yes, but they should join at a common point. There shouldn't be any
other branches such as radiator returns between there and the boiler.

No there aren't (what would happen if there were?)

Google using 'central heating reverse circulation' and all will be
explained in several places. the point is that the HW return must
either be at the boiler or the last connection before the boiler.

If you are installing a bypass, then there is a correct position for
that as well.


I have two 15mm rad returns, one 22mm hw return and 22mm to the
boiler, so I'm going to need a couple of 22-15-22 or 22-22-15 tees.
Does it matter which?

The third figure is the dimension of the branch.

You choose according to the directions from which the pipes come. If
you're asking whether it's OK for the return to go through 90 degrees
and for a radiator return to join at that point i.e. 22 x 15 x 22 tee
then yes it is, as long as the ordering is correct.





Thanks.

On 2008-01-27 12:29:34 +0000, Fred said:

On Sun, 27 Jan 2008 11:48:31 -0000, "Roger Mills"
wrote:

So you'll have just one pair of boiler connections, with the pipes between
the boiler and airing cupboard being shared by both circuits?

Yes.

If you are
contemplating having both circuits running at the same time, there is a
*possibility* that the HW circuit may hog all the flow and starve the CH

That's what had worried me.

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

They can be combined, and this is usual in a fully-pumped system. The
important thing to make sure of is that *all* of the radiator returns are
combined into a single pipe before it joins into the HW return.

Can I have two rad returns join the HW return in a tee or should I tee
the two rad returns together first?

You would probably get away with it, but it's safer to bring *all*
heating returns together first rather than to do that.


Otherwise you may get odd things - such as reverse circulation -
occurring under some
circumstances.

Out of interest, what circumstances would cause that?

Certain cases of HW demand and a differential in pressure created
between two points through which the HW return flow would be going.
It's effectively the same mechanism that causes pumping over into the
header tank if the feed and vent pipes are too far apart.




Thanks.

In article ,
Fred writes:
On Sun, 27 Jan 2008 08:43:38 +0000, Andy Hall
wrote:

Can I join the HW and CH return into one 22m pipe or should they have
separate returns to the boiler?

Yes, but they should join at a common point. There shouldn't be any
other branches such as radiator returns between there and the boiler.

No there aren't (what would happen if there were?)

The pressure difference between the common point and where
a radiator taps back in will create a small flow through
the heating system when it's off and the H/W circuit is on.
This would be annoying in Summer.

I have this with mine, but as both circuits are heating
zones, it doesn't matter. Upstairs rads get slightly warm
just on the top edge when downstairs heating zone is on,
because one of the upstairs radiators returns at the boiler
rather than the comon point. (It vasty simplified the plumbing,
by allowing me to reuse a retired gas pipe for the flow
and not have to rip up yet another room to lay a return
pipe.)

I have two 15mm rad returns, one 22mm hw return and 22mm to the
boiler, so I'm going to need a couple of 22-15-22 or 22-22-15 tees.
Does it matter which?

I would combine the 15mm rad returns into a 22mm, and then
combine the three 22mm in an equal T. Then you can't have
any pressure differential between the two radiator returns.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In an earlier contribution to this discussion,
Fred wrote:


Can I have two rad returns join the HW return in a tee or should I tee
the two rad returns together first?


As I said earlier, you need to join *all* the rad returns together *before*
combining them with the HW return.

Otherwise you may get odd things - such as reverse circulation -
occurring under some circumstances.

Out of interest, what circumstances would cause that?


If you have CH heating returns joining into the HW return at two different
places, you have an alternative flow path for some of the HW flow - which
can go backwards through one lot of rads and then forwards through the other
lot, back to to the HW pipe. This can happen even with the CH zone valve
closed - so your rads may get hot when you're heating the HW when you don't
want them to, like in the summer.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sun, 27 Jan 2008 12:26:50 -0000, "Roger Mills"
wrote:

Surely that's determined by the pipe layout - i.e. whether or not the 22mm
pipe turns through a right angle at the connection point. Actually, I think
I might be tempted to use 22x22x22 tees plus 22x15 reducers a little way
along the CH pipes.

I have used a 22-22-22 as you suggested.

The problem I have hit now is that the pipes going to the cylinder
were 22mm with a special "thing" on them (it looked like a washer or
flat olive) that allowed them to be inserted into the 1" fitting.

How can I plumb the new pipes to the cylinder? I've just dashed out
before the shops close and have collected a few things. One is a 1"
female to 22 mm compression couple. Can I just screw that onto the
cylinder with a bit of ptfe tape inside?

Or can I use 28mm pipe and a 28mm olive into the 1" fitting. Is a 1"
nut the same as a 28mm nut? I seem to remember reading something like
that here before because IIRC the 28mm is the external diameter
whereas the 1" was the internal one? Do I need a special 1" olive or
am I getting confused with 22mm and 3/4" fittings?

Thanks again.

On Sun, 27 Jan 2008 12:38:26 +0000, Andy Hall
wrote:

If you are installing a bypass, then there is a correct position for
that as well.

I might be. There seems some controversy over whether I need one.
Where should it be? The pump is now in the airing cupboard. If I have
to run a new pipe back to the boiler for the bypass, I may not be
bothered! I was hoping to fit the end to the HW out on the cylinder
but I guess you'll tell me that's wrong ;(

On Sun, 27 Jan 2008 15:03:11 -0000, "Roger Mills"
wrote:

As I said earlier, you need to join *all* the rad returns together *before*
combining them with the HW return.

If you have CH heating returns joining into the HW return at two different
places, you have an alternative flow path for some of the HW flow - which
can go backwards through one lot of rads and then forwards through the other
lot, back to to the HW pipe. This can happen even with the CH zone valve
closed - so your rads may get hot when you're heating the HW when you don't
want them to, like in the summer.

The boiler is downstairs. It has two pairs of connections: one 28 pair
for HW and one 22 pair for CH but I think these are joined inside the
boiler. So even if the two returns were kept separate, what is to stop
some hot water "leaking" from the HW side into the CH return in
summer?

I was going to tee the upstairs radiator return into the HW return.
Now I'm not so sure. I was being lazy and trying to avoid running
another pipe downstairs. Would you suggest I run the upstairs CH
return to the boiler separately?

Thanks.

On Sun, 27 Jan 2008 08:43:38 +0000, Andy Hall
wrote:

It's also important to make sure that the feed/expansion pipe and the
vent pipe are not on opposite sides of the pump or even opposite sides
of the boiler. If they are on a pipe run, then no more than 150mm
apart.

Sorry, I am confused by this.

The feed pipe runs from the header tank to the cylinder where it tees
into the HW return and runs back to the boiler.

The vent tees off the HW from the boiler where it goes into the
cylinder.

I will put the valves and pumps after the vent but I am unsure where
the 150mm comes into it?

Thanks.

On 2008-01-27 16:02:31 +0000, Fred said:

On Sun, 27 Jan 2008 12:26:50 -0000, "Roger Mills"
wrote:

Surely that's determined by the pipe layout - i.e. whether or not the 22mm
pipe turns through a right angle at the connection point. Actually, I think
I might be tempted to use 22x22x22 tees plus 22x15 reducers a little way
along the CH pipes.

I have used a 22-22-22 as you suggested.

The problem I have hit now is that the pipes going to the cylinder
were 22mm with a special "thing" on them (it looked like a washer or
flat olive) that allowed them to be inserted into the 1" fitting.

How can I plumb the new pipes to the cylinder? I've just dashed out
before the shops close and have collected a few things. One is a 1"
female to 22 mm compression couple. Can I just screw that onto the
cylinder with a bit of ptfe tape inside?

Usually quite a bit because often the threads are a little on the loose side.

Wrap on the male thread of the cylinder fitting in a clockwise
direction as you look at it. The point is not to unwind the tape as
you screw on the fitting



Or can I use 28mm pipe and a 28mm olive into the 1" fitting. Is a 1"
nut the same as a 28mm nut? I seem to remember reading something like
that here before because IIRC the 28mm is the external diameter
whereas the 1" was the internal one? Do I need a special 1" olive or
am I getting confused with 22mm and 3/4" fittings?

What was there before? If it was a compression fitting then it ought
to be used as that again.




Thanks again.

On 2008-01-27 16:04:54 +0000, Fred said:

On Sun, 27 Jan 2008 12:38:26 +0000, Andy Hall
wrote:

If you are installing a bypass, then there is a correct position for
that as well.

I might be. There seems some controversy over whether I need one.
Where should it be? The pump is now in the airing cupboard. If I have
to run a new pipe back to the boiler for the bypass, I may not be
bothered! I was hoping to fit the end to the HW out on the cylinder
but I guess you'll tell me that's wrong ;(

This was a gravity system, so the cylinder previously was the bypass -
i.e. any spare heat when the boiler stops firing circulates up to that.

Now you are taking that away and replacng it with a pump followed by
one or two motorised valves. There isn't really anywhere for the heat
to go and the boiler may object to that.

The starting point would be to check the boiler documentation if you
have it, or the manufacturer web site or call the manufacturer and find
out of a bypass is required. If it isn't then there is nothing to do.

If there is a requirement, then the usual way is to fit a lockshield
valve between a point just after the pump and a point after the joining
point for the CH and HW returns. It is set to part open. Then when
the motorised valve closes, there is a way for the water to circulate,
albeit in a shorter path than normal. If a boiler does require a
bypass, it normally has a pump over-run thermostat which keeps the pump
running until after the water in the boiler drops below a certain
temperature. This should be obvious from the wiring arrangement.

A slightly better solution is to use an automatic bypass valve. These
go in the same position as the lockshield but have an adjustable spring
to hold them closed. They remain closed when the motorised valve is
open but open when the pressure rises as a result of the pump being on
and the valve closed.

On 2008-01-27 16:28:20 +0000, Fred said:

On Sun, 27 Jan 2008 08:43:38 +0000, Andy Hall
wrote:

It's also important to make sure that the feed/expansion pipe and the
vent pipe are not on opposite sides of the pump or even opposite sides
of the boiler. If they are on a pipe run, then no more than 150mm
apart.

Sorry, I am confused by this.

The feed pipe runs from the header tank to the cylinder where it tees
into the HW return and runs back to the boiler.

The vent tees off the HW from the boiler where it goes into the
cylinder.

I will put the valves and pumps after the vent but I am unsure where
the 150mm comes into it?

Thanks.

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.

If the FE and the vent pipes are joined to a point on the circuit where
they are close together, then the recommendation is for the two
connecting points not to be more than 150mm apart. That way, you can't
have a great enough pressure for anything bad to happen.

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. Effectively, you would remove the
vent pipe from the old HW side of the boiler and move it to the CH
side. The important point is that there is nothing between the boiler
and the vent like any pumps or valves. This approach also has the
advantage that after filling, air bubbles are expelled very quickly and
easily and bleeding is less of an issue. This would leave you
with a high point on the cylinder connection, probably. To that point,
you would fit an air vent - either a manual one worked with a key or an
automatic one.

On 2008-01-27 16:25:19 +0000, Fred said:

On Sun, 27 Jan 2008 15:03:11 -0000, "Roger Mills"
wrote:

As I said earlier, you need to join *all* the rad returns together *before*
combining them with the HW return.

If you have CH heating returns joining into the HW return at two different
places, you have an alternative flow path for some of the HW flow - which
can go backwards through one lot of rads and then forwards through the other
lot, back to to the HW pipe. This can happen even with the CH zone valve
closed - so your rads may get hot when you're heating the HW when you don't
want them to, like in the summer.

The boiler is downstairs. It has two pairs of connections: one 28 pair
for HW and one 22 pair for CH but I think these are joined inside the
boiler. So even if the two returns were kept separate, what is to stop
some hot water "leaking" from the HW side into the CH return in
summer?

I was going to tee the upstairs radiator return into the HW return.
Now I'm not so sure. I was being lazy and trying to avoid running
another pipe downstairs. Would you suggest I run the upstairs CH
return to the boiler separately?

Thanks.

It's probably best at this point to sketch out the whole thing and
figure out whether you will be breaking the rules over where the pipes
join. For example, it may well be the case that you will need to
join everything to a point leading to the old CH side and do away with
the HW side of the boiler altogether, simply plugging the taps.

On Sun, 27 Jan 2008 16:46:46 +0000 someone who may be Andy Hall
wrote this:-

A slightly better solution is to use an automatic bypass valve. These
go in the same position as the lockshield but have an adjustable spring
to hold them closed. They remain closed when the motorised valve is
open but open when the pressure rises as a result of the pump being on
and the valve closed.

Definitely the thing to install on a new system, assuming that the
boiler manufacturer does not have some special requirement.



--
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:

On Sun, 27 Jan 2008 15:03:11 -0000, "Roger Mills"
wrote:

As I said earlier, you need to join *all* the rad returns together
*before* combining them with the HW return.

If you have CH heating returns joining into the HW return at two
different places, you have an alternative flow path for some of the
HW flow - which can go backwards through one lot of rads and then
forwards through the other lot, back to to the HW pipe. This can
happen even with the CH zone valve closed - so your rads may get hot
when you're heating the HW when you don't want them to, like in the
summer.

The boiler is downstairs. It has two pairs of connections: one 28 pair
for HW and one 22 pair for CH but I think these are joined inside the
boiler. So even if the two returns were kept separate, what is to stop
some hot water "leaking" from the HW side into the CH return in
summer?

I was going to tee the upstairs radiator return into the HW return.
Now I'm not so sure. I was being lazy and trying to avoid running
another pipe downstairs. Would you suggest I run the upstairs CH
return to the boiler separately?

Thanks.

Hang on a bit! For a fully pumped system with a single pump, you *can't*
have two pairs of pipes connected to the boiler - you must have *only* one
flow pipe as far as the pump, but you can have separate HW and CH returns -
making a maximum of *three* connections.

It sounds as if you have separate upstairs and downstairs CH circuits -
probably teeing off near the boiler connections? If that is the case, you
must disconnect the CH flow pipe at the boiler, and blank off the boiler
connection. 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.

As stated before, the rad returns - and that includes both upstairs and
downstairs - must all join together before joining into the HW return or -
if it's easier - they can go all the way to the boiler and not join into the
HW return at all. From my current perception of your setup, that probably
would be easier. Unless I'm mistaken, you already have CH returns from both
floors going back to the boiler, and joining together just before the boiler
connection. If that's the case, leave that bit as it is - apart from
inserting a bit of pipe where the pump used to be.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sun, 27 Jan 2008 16:25:19 GMT someone who may be Fred
wrote this:-

The boiler is downstairs. It has two pairs of connections: one 28 pair
for HW and one 22 pair for CH but I think these are joined inside the
boiler.

They certainly are. Otherwise how could the central heating circuit
be filled up?

In that situation I would add a second pump for the hot water and
have a two pump system. No motorised valves to go wrong and easy to
adjust with the pump speeds. If the existing pump was in good
condition I would move it to the hot water circuit and replace it
with a smart pump on the heating.

With such a setup the position of the vent pipe and feed & expansion
pipe might not be so critical. I might even try it and see if I
could get away with it without pumping over.


--
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,
Andy Hall wrote:


This was a gravity system, so the cylinder previously was the bypass -
i.e. any spare heat when the boiler stops firing circulates up to
that.
Now you are taking that away and replacng it with a pump followed by
one or two motorised valves. There isn't really anywhere for the
heat to go and the boiler may object to that.

The starting point would be to check the boiler documentation if you
have it, or the manufacturer web site or call the manufacturer and
find out of a bypass is required. If it isn't then there is nothing
to do.
If there is a requirement, then the usual way is to fit a lockshield
valve between a point just after the pump and a point after the
joining point for the CH and HW returns. It is set to part open. Then
when the motorised valve closes, there is a way for the water to
circulate, albeit in a shorter path than normal. If a boiler does
require a bypass, it normally has a pump over-run thermostat which
keeps the pump running until after the water in the boiler drops
below a certain temperature. This should be obvious from the
wiring arrangement.
I suppose it's possible that the boiler may require pump over-run if used in
a fully pumped system, but not when in a gravity system. It obviously can't
over-run the pump in a gravity system 'cos when only the HW is being heated,
the pump ain't running at all!

As you say, a gravity HW system would act as a sort of by-pass (gravity flow
only) to get rid of some of the boiler's heat. A manual by-pass circuit
would also allow some gravity flow when both zone valves are closed - but
there's no way that gravity flow would generate sufficient pressure to open
an automatic by-pass. So unless the boiler explicitly requires a pump
over-run in a fully-pumped situation and controls the pump - there's no
point in having an automatic by-pass valve.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On 2008-01-27 17:45:24 +0000, "Roger Mills" said:

I suppose it's possible that the boiler may require pump over-run if used in
a fully pumped system, but not when in a gravity system. It obviously can't
over-run the pump in a gravity system 'cos when only the HW is being heated,
the pump ain't running at all!

As you say, a gravity HW system would act as a sort of by-pass (gravity flow
only) to get rid of some of the boiler's heat. A manual by-pass circuit
would also allow some gravity flow when both zone valves are closed - but
there's no way that gravity flow would generate sufficient pressure to open
an automatic by-pass. So unless the boiler explicitly requires a pump
over-run in a fully-pumped situation and controls the pump - there's no
point in having an automatic by-pass valve.

Exactly, which was why the starting point is to find out whether the
manufacturer says that a bypass is needed.

I would expect him to say that either

- no bypass is needed ever

- bypass is needed if circuit is pumped and no gravity is used and then
provide an over-run thermostat

- boiler can't be used other than with gravity as part of the installation

On Sun, 27 Jan 2008 17:40:22 +0000, David Hansen
wrote:

In that situation I would add a second pump for the hot water and
have a two pump system. No motorised valves to go wrong and easy to
adjust with the pump speeds. If the existing pump was in good
condition I would move it to the hot water circuit and replace it
with a smart pump on the heating.

What is a smart pump?

In an earlier contribution to this discussion,
Fred wrote:

On Sun, 27 Jan 2008 17:40:22 +0000, David Hansen
wrote:

In that situation I would add a second pump for the hot water and
have a two pump system. No motorised valves to go wrong and easy to
adjust with the pump speeds. If the existing pump was in good
condition I would move it to the hot water circuit and replace it
with a smart pump on the heating.

What is a smart pump?

A pump - such as a Grunfoss Alpha - which varies its output depending on the
resistance in the system. Typically used on CH systems which have TRVs on
most radiators. When most of the TRVs are shut, so that the system flow
resistance increases, an ordinary pump would build up a lot more pressure,
whereas a 'smart' pump will back off. In simple terms, it's attempting to
produce a more or less constant pressure regardless of flow - although it
can't *quite* achieve that.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sun, 27 Jan 2008 17:34:50 -0000, "Roger Mills"
wrote:

Hang on a bit! For a fully pumped system with a single pump, you *can't*
have two pairs of pipes connected to the boiler - you must have *only* one
flow pipe as far as the pump, but you can have separate HW and CH returns -
making a maximum of *three* connections.

Sorry I was explaining what connections were on the boiler, used or
not. You are quite right that I am using three of the four.

It sounds as if you have separate upstairs and downstairs CH circuits -
probably teeing off near the boiler connections? If that is the case, you
must disconnect the CH flow pipe at the boiler, and blank off the boiler
connection. 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.

That's what I've done. So far so good.

As stated before, the rad returns - and that includes both upstairs and
downstairs - must all join together before joining into the HW return or -
if it's easier - they can go all the way to the boiler and not join into the
HW return at all. From my current perception of your setup, that probably
would be easier. Unless I'm mistaken, you already have CH returns from both
floors going back to the boiler, and joining together just before the boiler
connection. If that's the case, leave that bit as it is - apart from
inserting a bit of pipe where the pump used to be.

I took out the pipes because they were touching each other with no
room for lagging. I have put three back, with lagging, but I haven't
re-laid the fourth. I was hoping not to, and share the HW return, but
it looks as though I must?

Thanks.

On 2008-01-27 18:04:19 +0000, Fred said:

On Sun, 27 Jan 2008 17:40:22 +0000, David Hansen
wrote:

In that situation I would add a second pump for the hot water and
have a two pump system. No motorised valves to go wrong and easy to
adjust with the pump speeds. If the existing pump was in good
condition I would move it to the hot water circuit and replace it
with a smart pump on the heating.

What is a smart pump?

e.g. Grundfos Alpha - sets itself.

In an earlier contribution to this discussion,
Fred wrote:


I took out the pipes because they were touching each other with no
room for lagging. I have put three back, with lagging, but I haven't
re-laid the fourth. I was hoping not to, and share the HW return, but
it looks as though I must?

Thanks.

'Fraid so! You *could* bring the downstairs return up to the airing cupboard
and merge it with the upstairs return before connecting them into the HW
return - but you'd *still* need the fourth pipe, and the downstairs water
would have further to travel - so there's not much point. So take the
upstairs return down, and merge it with the downstairs return before
connecting the merged returns into the boiler.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

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


A pump - such as a Grunfoss Alpha - which varies its output depending on the
resistance in the system. Typically used on CH systems which have TRVs on
most radiators. When most of the TRVs are shut, so that the system flow
resistance increases, an ordinary pump would build up a lot more pressure,
whereas a 'smart' pump will back off. In simple terms, it's attempting to
produce a more or less constant pressure regardless of flow - although it
can't *quite* achieve that.

Interesting. Does this mean that a bypass valve is not required in a
system with such a pump?

Someone said something about when the boiler switches off, the hot
water in the boiler will want to rise somewhere so would I need a
bypass valve for that regardless of whether or not I have a smart
pump? Surely any boiler that would be damaged if the water cannot rise
would need an over-run anyway?

I've added the fourth pipe as per your other post. I'm unsure where I
would fit a bypass to. Since the pump is in the airing cupboard, can I
tee into the HW return (also in the airing cupboard) or must I run a
fifth pipe downstairs?

Thanks.

On Sun, 27 Jan 2008 16:46:46 +0000, Andy Hall
wrote:

The starting point would be to check the boiler documentation if you
have it, or the manufacturer web site or call the manufacturer and find
out of a bypass is required. If it isn't then there is nothing to do.

It's a mistral oil fired boiler. Are they still made? The instructions
left by the previous people look quite old and are nothing but an A3
page with specification on.

Does anyone know if Mistral exist, and if so how I can get in touch
with them or whether the bypass is required with this boiler?

Thanks.

On Mon, 28 Jan 2008 07:29:08 GMT someone who may be Fred
wrote this:-

A pump - such as a Grunfoss Alpha - which varies its output depending on the
resistance in the system. Typically used on CH systems which have TRVs on
most radiators. When most of the TRVs are shut, so that the system flow
resistance increases, an ordinary pump would build up a lot more pressure,
whereas a 'smart' pump will back off. In simple terms, it's attempting to
produce a more or less constant pressure regardless of flow - although it
can't *quite* achieve that.

Interesting. Does this mean that a bypass valve is not required in a
system with such a pump?

The type of pump makes no difference. A smart pump will only go down
to a minimum speed.

I do think that a drawing would help people understand the current
and proposed systems.


--
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:

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


A pump - such as a Grunfoss Alpha - which varies its output
depending on the resistance in the system. Typically used on CH
systems which have TRVs on most radiators. When most of the TRVs are
shut, so that the system flow resistance increases, an ordinary pump
would build up a lot more pressure, whereas a 'smart' pump will back
off. In simple terms, it's attempting to produce a more or less
constant pressure regardless of flow - although it can't *quite*
achieve that.

Interesting. Does this mean that a bypass valve is not required in a
system with such a pump?


No really - the two are not directly related. A by-pass circuit doesn't
protect the pump (most pumps will happily run stalled anyway) but protects
the boiler by providing a flow path to enable residual heat to be
dissipated.


Someone said something about when the boiler switches off, the hot
water in the boiler will want to rise somewhere so would I need a
bypass valve for that regardless of whether or not I have a smart
pump? Surely any boiler that would be damaged if the water cannot rise
would need an over-run anyway?

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, and invariably directly control the pump -
keeping it running for a while after the boiler stops firing. There needs to
be an open flow path during this 'pump-over-run' phase - which is where a
by-pass circuit comes in, to provide a path when all the zone valves are
closed.

Older boilers are often physically larger, and hold more water - and are
much less in danger of overheating when the flame is suddenly cut. The fact
that yours has happily worked with an un-pumped HW circuit suggests that
it's in this category. It *probably* doesn't need a by-pass but - as Andy H
suggests - you really need to study the installation manual, or contact the
manufacturer to determine whether there are any specific installation
requirements, depending on whether it's being used in a gravity or fully
pumped system. In a gravity system, there is always a flow path open -
albeit convection flow only. With your re-arranged system there will be *no*
flow path when both zone valves are closed. Only the boiler manufacturer
will know whether this matters and, if so, what to do about it.


I've added the fourth pipe as per your other post. I'm unsure where I
would fit a bypass to. Since the pump is in the airing cupboard, can I
tee into the HW return (also in the airing cupboard) or must I run a
fifth pipe downstairs?

Thanks.



--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

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?

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?

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

Thanks again.

In an earlier contribution to this discussion,
Roger Mills wrote:

In an earlier contribution to this discussion,
Fred wrote:



I've added the fourth pipe as per your other post. I'm unsure where I
would fit a bypass to. Since the pump is in the airing cupboard, can
I tee into the HW return (also in the airing cupboard) or must I run
a fifth pipe downstairs?

Thanks.

Sorry, I hit Send too soon in my last post, before I had replied to this
paragraph.

I see no reason why the by-pass can't simply be in parallel with the HW zone
valve and heating coil - i.e. connected into the flow pipe just after the
pump but before the zone valves, and returning into the HW return. I don't
think you need a fifth pipe back to the boiler.

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. So a manual by-pass may be your only option. The
problem with manual by-passes is that they are always open, and partially
short-circuit the HW and CH circuits even when not needed. At least there
would always be a flow path (if the boiler needs one - which is by no means
certain) and it would allow gravity circulation akin to what you previously
had.

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. This
would have the effect that, when the boiler and pump demand are cut, the
timer would keep the pump running for a couple of minutes, the bypass (if
correctly set) would open, and any residual heat would be carried away from
the boiler.

[1] Such as http://www.tlc-direct.co.uk/Products/BGDT20.html
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On 2008-01-28 07:29:08 +0000, Fred said:

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


A pump - such as a Grunfoss Alpha - which varies its output depending on the
resistance in the system. Typically used on CH systems which have TRVs on
most radiators. When most of the TRVs are shut, so that the system flow
resistance increases, an ordinary pump would build up a lot more pressure,
whereas a 'smart' pump will back off. In simple terms, it's attempting to
produce a more or less constant pressure regardless of flow - although it
can't *quite* achieve that.

Interesting. Does this mean that a bypass valve is not required in a
system with such a pump?

No it doesn't. Where is is helpful, is if you have TRVs. As the
valves close because the place is warm enough, the pump will begin to
reduce output.

If you need a bypass valve, you need one.



Someone said something about when the boiler switches off, the hot
water in the boiler will want to rise somewhere so would I need a
bypass valve for that regardless of whether or not I have a smart
pump? Surely any boiler that would be damaged if the water cannot rise
would need an over-run anyway?

It really depends on the boiler. The case that you are trying to
cover is that the room or cylinder thermostat is satisfied and cuts off
when the boiler is hot and burning. The burner is stopped
instantly. However, without over-run and circulation to somewhere to
dump the heat, the temperature of the water may rise to boiling point
or close to it producing noise and perhaps steam. You don't really
want that.

This is more likely to be an issue with boilers having a high thermal
mass - e.g. cast iron because there is more retained heat. Newer
boilers tend to have low thermal mass and low water content and it's
less of an issue. For example, on mine, the pump is inside the boiler
and the heat exchanger is stainless steel with a coiled tube inside.
The bypass is a short length of thin tube inside the case of the boiler
itself. Normally, the boiler is operating the motorised valves and
is able to dump excess heat into the circuit immediately after closing
down. However, if that isn't possible, there is enough by simply
continuing to circulate the water inside the boiler.

That's why you really need to find out from the manufacturer what they require.


I've added the fourth pipe as per your other post. I'm unsure where I
would fit a bypass to. Since the pump is in the airing cupboard, can I
tee into the HW return (also in the airing cupboard) or must I run a
fifth pipe downstairs?

This is getting complicated. On the flow side, the bypass needs to
come from a point after the pump and before the motorised valve(s).
It should really be returned to a point after the CH and HW have been
joined together. If that is effectively at the boiler because you are
doing the final joining of these circuits are parts thereof at the
boiler, then theoretically you need a pipe for it. However, the flow
through the bypass will be throttled down anyway if you use a
lockshield, so if there is any reverse circulation, it will not be
much. There is an easier path through the main circuit. If you use
an automatic bypass valve, it will only open for the couple of minutes
after the boiler has been firing and the CH and HW thermostats are off.
i.e. you won't really notice the effect - a couple of radiators might
become briefly warm.


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.







Thanks.

On Mon, 28 Jan 2008 09:05:23 GMT, Fred wrote:

It's a mistral oil fired boiler. Are they still made?
snip
Does anyone know if Mistral exist, and if so how I can get in touch
with them or whether the bypass is required with this boiler?

We have a Mistral oil fired jobbie, floor standing about 4 x 2 x 3 feet
containing a fecking great lump of cast iron holding 12 gallons of
water... A bypass isn't required like it is for small high themal output,
low volume boilers that literally melt if they don't have a bypass and
pump over run.

Ours needs overun but that beacause it is a monster 38kW output with,
under mosts circumstances, a much smaller load so it tends to trip it's
overheat stat. If yours is better matched to the system I expect it'll be
fine without a bypass. With the proviso that the control system won't have
the pump running into a shutdown system.

I recently had a dig about on the web for Mistral. I'm not sure they are
still trading as such, they last address/phone number I have are Telford
based. Google is your friend.

--
Cheers
Dave. pam is missing e-mail