Hello,

We've got a gravity fed CH system. I think you call it plan C. I don't
know everything because much of it is hidden under the floor or behind
boxes but it seems as though we have 28mm pipe from the boiler to the
cyclinder. There is only one pump (next to the boiler) and no valves.
The pump is energised by the room thermostat for the CH. There is no
cylinder stat. We can have HW only or HW and CH but not CH only. Does
this sound about right?

A neighbour has just paid thousands to have his system converted so
that HW and CH may be switched separately. Is it worth us doing the
same (the converting, not the paying thousands!)

Is it just a matter of inserting a valve and a bypass to control
whether the hot water goes to the cylinder only or carries on to the
radiators? What else is involved?

Thanks.

On Mon, 17 Sep 2007 16:48:13 +0000, nospam wrote:

Hello,

We've got a gravity fed CH system. I think you call it plan C. I don't
know everything because much of it is hidden under the floor or behind
boxes but it seems as though we have 28mm pipe from the boiler to the
cyclinder. There is only one pump (next to the boiler) and no valves.
The pump is energised by the room thermostat for the CH. There is no
cylinder stat. We can have HW only or HW and CH but not CH only. Does
this sound about right?

A neighbour has just paid thousands to have his system converted so
that HW and CH may be switched separately. Is it worth us doing the
same (the converting, not the paying thousands!)

Is it just a matter of inserting a valve and a bypass to control
whether the hot water goes to the cylinder only or carries on to the
radiators? What else is involved?

This work would normally be done as part of a package of upgrading the
heating system including a new boiler. There is no reason why you couldn't
improve the existing arrangements. We have discussed heating over and over
on this ng.
The FAQs below, The wiki and the subject of C-plan should get you started.


--
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

On Mon, 17 Sep 2007 17:10:37 +0000 (UTC), Ed Sirett
wrote:

We have discussed heating over and over
on this ng.
The FAQs below, The wiki and the subject of C-plan should get you started.


Thanks. I had already found and read the faq which pointed me to the
Honeywell site. The faq is great but I needed to see the pictures at
Honeywell. Where do I find the wiki?

On Wed, 19 Sep 2007 08:32:34 GMT, nospam wrote:

Where do I find the wiki?


Sorry to answer my own question but is it:
http://www.wiki.diyfaq.org.uk ?

On Mon, 17 Sep 2007 16:48:13 GMT someone who may be nospam
wrote this:-

We've got a gravity fed CH system. I think you call it plan C. I don't
know everything because much of it is hidden under the floor or behind
boxes but it seems as though we have 28mm pipe from the boiler to the
cyclinder. There is only one pump (next to the boiler) and no valves.
The pump is energised by the room thermostat for the CH. There is no
cylinder stat. We can have HW only or HW and CH but not CH only. Does
this sound about right?

It sounds like the hot water is heated by gravity circulation of
primary water. Fairly standard a long time ago, but increasingly
uncommon.

A neighbour has just paid thousands to have his system converted so
that HW and CH may be switched separately.

It is worth converting to a fully pumped system. It sounds like your
neighbour had a lot more done, or he was diddled.

Is it just a matter of inserting a valve and a bypass to control
whether the hot water goes to the cylinder only or carries on to the
radiators?

No. The pipe that circulates primary water to the hot water cylinder
almost certainly continues to form the expansion pipe. You can
probably see this if you look at the cylinder connections and follow
the pipes.

Installing a valve that will shut this pipe converts the heating
system into one which has inadequate provision to cope with the
expansion of the water as it heats up. The end result tends to be a
loud bang and lots of very hot water being flung around.


--
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 Mon, 17 Sep 2007 18:15:59 +0100, David Hansen
wrote:

A neighbour has just paid thousands to have his system converted so
that HW and CH may be switched separately.

It is worth converting to a fully pumped system. It sounds like your
neighbour had a lot more done, or he was diddled.

I'm not sure exactly what he had done nor exactly how much he paid. I
saw a new cylinder being carried in too. Perhaps he went fully pumped?
What are the advantages of this: the HW gets hot quicker?

"nospam" wrote


I'm not sure exactly what he had done nor exactly how much he paid. I
saw a new cylinder being carried in too. Perhaps he went fully pumped?
What are the advantages of this: the HW gets hot quicker?

Absolutely!
I had to re-program my parent's time clock recently and noticed that the hot
water was timed to come on with the heating in the morning (for 3-4 hours).
Thinking this was a mistake, I reduced this to 1/2 hour like my pumped
system.
The next day they rang to complain of no hot water!
Had to increase the time back upto 3 hours IIRC as they have gravity
circulation from back boiler.

Phil

In an earlier contribution to this discussion,
nospam wrote:

Hello,

We've got a gravity fed CH system. I think you call it plan C. I don't
know everything because much of it is hidden under the floor or behind
boxes but it seems as though we have 28mm pipe from the boiler to the
cyclinder. There is only one pump (next to the boiler) and no valves.
The pump is energised by the room thermostat for the CH. There is no
cylinder stat. We can have HW only or HW and CH but not CH only. Does
this sound about right?

A neighbour has just paid thousands to have his system converted so
that HW and CH may be switched separately. Is it worth us doing the
same (the converting, not the paying thousands!)

Is it just a matter of inserting a valve and a bypass to control
whether the hot water goes to the cylinder only or carries on to the
radiators? What else is involved?

Thanks.

Whatever you've got, it ain't a C-Plan - because that would have a valve and
a cylinder stat, and would permit CH without HW if desired.

How many pipes are connected to the boiler? My guess is that there are
four - two for the gravity HW circuit and two more for the pumped CH
circuit.

If that is the case, you can convert it to a C-Plan, which will give you
independent control over the HW and CH - albeit not quite as efficiently as
as a fully-pumped system, but nevertheess a lot better that what you
currently have.

All you need is a 28mm 2-port valve of the right type (see the C-Plan
diagram on the Honeywell site) and a cylinder stat. As others have
indicated, you have to be careful where you insert the valve so that it
never prevents the boiler from having a clear path to the expansion tank. If
the pipe to the expansion tank tees off near the HW cylinder, the valve
needs to be on the *cylinder* side of the tee. You'll probably also find
that your programmer has a link fitted which forces the HW on whenever the
CH is on in order to ensure that the boiler runs for the CH, 'cos the room
stat only controls the pump. But if you re-wire as necessary to comply with
the C-Plan diagram, you should be ok.

If you're doing it youself, it should cost you less than £100 for the bits.
--
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, 17 Sep 2007 19:18:41 +0100, "Roger Mills"
wrote:

Whatever you've got, it ain't a C-Plan - because that would have a valve and
a cylinder stat, and would permit CH without HW if desired.

Hello,

You are quite right that it isn't a C-plan. I thought the C-plamn was
the simplest set-up but I re-read the Honeywell site and the C-plan
does have a valve; so my set-up is not C-plan but something even more
basic.

How many pipes are connected to the boiler? My guess is that there are
four

Yes there are.

If that is the case, you can convert it to a C-Plan, which will give you
independent control over the HW and CH

All you need is a 28mm 2-port valve of the right type (see the C-Plan
diagram on the Honeywell site) and a cylinder stat.

The cyclinder is covered in foam insulation. Do I just carefully cut
out a chunk to fasten a cylinder stat to? Then wire the cylinder stat
to the controller.

What is the function of this? Does it switch off the boiler when the
HW is at the right temperature?

I will have another look at the Honeywell site to see where the valve
should go.

[snip]

You'll probably also find
that your programmer has a link fitted which forces the HW on whenever the
CH is on in order to ensure that the boiler runs for the CH

Correct again.

On 2007-09-19 09:28:36 +0100, nospam said:

On Mon, 17 Sep 2007 19:18:41 +0100, "Roger Mills"
wrote:

Whatever you've got, it ain't a C-Plan - because that would have a valve and
a cylinder stat, and would permit CH without HW if desired.

Hello,

You are quite right that it isn't a C-plan. I thought the C-plamn was
the simplest set-up but I re-read the Honeywell site and the C-plan
does have a valve; so my set-up is not C-plan but something even more
basic.

How many pipes are connected to the boiler? My guess is that there are
four

Yes there are.

If that is the case, you can convert it to a C-Plan, which will give you
independent control over the HW and CH

All you need is a 28mm 2-port valve of the right type (see the C-Plan
diagram on the Honeywell site) and a cylinder stat.

The cyclinder is covered in foam insulation. Do I just carefully cut
out a chunk to fasten a cylinder stat to? Then wire the cylinder stat
to the controller.

Yes.


What is the function of this? Does it switch off the boiler when the
HW is at the right temperature?

The thermostat closes the valve to stop circulation around the gravity
loop and a switch on the valve switches off the boiler.

This is why you have to be careful where you install the valve - i.e.
not on the path from boiler to vent pipe.



I will have another look at the Honeywell site to see where the valve
should go.

That's a stylised diagram so be careful. Trace the pipes to the roof
tank and be sure that the valve is not between boiler and vent.

All of this set up only has the effect of saving some energy by
preventing the boiler cycling when the water is already hot.

If you want to improve performance, and you are installing a new
controller anyway, it's usually not much more work to convert to fully
pumped using a three way valve.

Then you can have completely separate CH and HW control as well as the
water heating more quickly.








[snip]

You'll probably also find
that your programmer has a link fitted which forces the HW on whenever the
CH is on in order to ensure that the boiler runs for the CH

Correct again.

In an earlier contribution to this discussion,
nospam wrote:

On Mon, 17 Sep 2007 19:18:41 +0100, "Roger Mills"
wrote:

Whatever you've got, it ain't a C-Plan - because that would have a
valve and a cylinder stat, and would permit CH without HW if desired.

Hello,

You are quite right that it isn't a C-plan. I thought the C-plamn was
the simplest set-up but I re-read the Honeywell site and the C-plan
does have a valve; so my set-up is not C-plan but something even more
basic.

Yes, you've got uncontrolled gravity hot water, and pumped CH. The HW heats
whenever the boiler is on, and will eventually get up to a scalding
temperature if you run the radiators hot.

How many pipes are connected to the boiler? My guess is that there
are
four

Yes there are.


Thought so!

If that is the case, you can convert it to a C-Plan, which will give
you independent control over the HW and CH

All you need is a 28mm 2-port valve of the right type (see the C-Plan
diagram on the Honeywell site) and a cylinder stat.

The cyclinder is covered in foam insulation. Do I just carefully cut
out a chunk to fasten a cylinder stat to? Then wire the cylinder stat
to the controller.

Yes. It's probably held in place with a piece of stretchy curtain wire round
the cylinder, which can go outside the foam - but the stat itself must make
metal to metal contact with the cylinder.

What is the function of this? Does it switch off the boiler when the
HW is at the right temperature?


In effect, though not directly. The cylinder stat opens the valve when the
HW needs to be heated, and allows it to close (by its spring return) when
the HW demand is satisfied. The actuator of the valve has a changeover
switch - which is electrically isolated from the motor circuit - which
changes position when the valve is fully open. This switch causes the boiler
to run via the room stat and pump when the valve is closed (CH only) and
causes just the boiler to run when the valve is open (HW only). If there is
a simultaneous demand for HW and CH, the switch on the valve controls the
boiler, and the room stat controls the pump. All very cunning - but it
*must* be wired exactly as per the Honeywell diagram if it is to work.
--
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, 17 Sep 2007 19:18:41 +0100, "Roger Mills"
wrote:

All you need is a 28mm 2-port valve of the right type (see the C-Plan
diagram on the Honeywell site) and a cylinder stat.

Sorry to post so many questions!

I have had another look at the cylinder. Two 28mm pipes come into the
airing cupboard. These are then reduced to 22mm pipe which connects to
the side of the cylinder. The one pipe has a tee: one side of the tee
connects to the cylinder, the other goes into the loft to vent in the
tank.

So it looks as if I need a 22mm valve which blocks the flow into the
cylinder but leaves the other side of the tee (boiler to vent) open at
all times: is that right?

The two pipes are not marked. Is the one with the tee piece the flow
into the cylinder and the lower one the flow out? Do you always put
the valve on the pipe with the tee?

I have looked at the Honeywell diagram and read the wiki but I am
still confused about one point. The diagram makes it look like a loop:
boiler to cylinder to radiators to boiler. If a valve stops flow at
the cylinder, won't it stop flow around the whole circuit? Doesn't
there need to be a bypass so that when the cylinder is blocked water
is diverted straight to the radiators?

Thanks.

On 2007-09-19 09:57:05 +0100, nospam said:

On Mon, 17 Sep 2007 19:18:41 +0100, "Roger Mills"
wrote:

All you need is a 28mm 2-port valve of the right type (see the C-Plan
diagram on the Honeywell site) and a cylinder stat.

Sorry to post so many questions!

I have had another look at the cylinder. Two 28mm pipes come into the
airing cupboard. These are then reduced to 22mm pipe which connects to
the side of the cylinder. The one pipe has a tee: one side of the tee
connects to the cylinder, the other goes into the loft to vent in the
tank.

So it looks as if I need a 22mm valve which blocks the flow into the
cylinder but leaves the other side of the tee (boiler to vent) open at
all times: is that right?

Yes that's it.


The two pipes are not marked. Is the one with the tee piece the flow
into the cylinder and the lower one the flow out? Do you always put
the valve on the pipe with the tee?

The thing is to avoid it being on the vent path and to make it only on
the cylinder path. Other than that it doesn't really matter.


I have looked at the Honeywell diagram and read the wiki but I am
still confused about one point. The diagram makes it look like a loop:
boiler to cylinder to radiators to boiler. If a valve stops flow at
the cylinder, won't it stop flow around the whole circuit? Doesn't
there need to be a bypass so that when the cylinder is blocked water
is diverted straight to the radiators?

The boiler will be fired up if either the HW or the CH demand heat.
Assuming that this is allowed by the timer, then the room thermostat
indirectly controls the pump running and demand to the boiler. If you
do the Cplan, the thermostat on the cylinder opens the valve and that
fires up the boiler.




Thanks.

On Wed, 19 Sep 2007 11:34:14 +0100, Andy Hall
wrote:

The boiler will be fired up if either the HW or the CH demand heat.
Assuming that this is allowed by the timer, then the room thermostat
indirectly controls the pump running and demand to the boiler. If you
do the Cplan, the thermostat on the cylinder opens the valve and that
fires up the boiler.

Thanks for your reply but I am confused about this: if the cylinder
stat says that the water is hot but the room thermostat says the room
is cold, won't this switch on the pump and close the valve? If so,
doesn't the water that goes through the radiators also circulate
through the cylinder to warm it? If the valve is closed, won't this
water be unable to move, damaging the pump and leaving the radiators
cold?

On 2007-09-19 13:13:32 +0100, nospam said:

On Wed, 19 Sep 2007 11:34:14 +0100, Andy Hall
wrote:

The boiler will be fired up if either the HW or the CH demand heat.
Assuming that this is allowed by the timer, then the room thermostat
indirectly controls the pump running and demand to the boiler. If you
do the Cplan, the thermostat on the cylinder opens the valve and that
fires up the boiler.

Thanks for your reply but I am confused about this: if the cylinder
stat says that the water is hot but the room thermostat says the room
is cold, won't this switch on the pump and close the valve?

yes.

If so,
doesn't the water that goes through the radiators also circulate
through the cylinder to warm it?

No. It should go through radiators only.

If the valve is closed, won't this
water be unable to move, damaging the pump and leaving the radiators
cold?

If you are doing Cplan, the branch to the radiators needs to be before
the cylinder and valve.

In effect this means that the CH circulation is based on whether or not
the pump is running and the HW on whether or not the valve is open.

The valve and branch to the pump need to be positioned appropriately
and the vent allowed either way.

That's why I said that it might be almost as easy to do a three way
valve and pump all of it.

In an earlier contribution to this discussion,
nospam wrote:

On Wed, 19 Sep 2007 11:34:14 +0100, Andy Hall
wrote:

The boiler will be fired up if either the HW or the CH demand heat.
Assuming that this is allowed by the timer, then the room thermostat
indirectly controls the pump running and demand to the boiler. If
you do the Cplan, the thermostat on the cylinder opens the valve and
that fires up the boiler.

Thanks for your reply but I am confused about this: if the cylinder
stat says that the water is hot but the room thermostat says the room
is cold, won't this switch on the pump and close the valve? If so,
doesn't the water that goes through the radiators also circulate
through the cylinder to warm it? If the valve is closed, won't this
water be unable to move, damaging the pump and leaving the radiators
cold?

No! You've got two separate circuits. One goes from the boiler to the
cylinder by gravity circulation, and back to the boiler. The other goes from
the boiler and is pumped round the radiators and back to the boiler. Closing
the valve stops the gravity circulation to the cylinder, but still allows
the pumped CH circuit to operate.

In general, you'll want your HW at about 60 degrees and the flow to your
radiators at 80 degrees. So the boiler has to operate at 80 degrees. As soon
as the water in the cylinder reaches 60 degrees (or wahatever the cylinder
stat is set to) the valve closes. The boiler can continue to heat the
radiators, but the HW doesn't get any hotter - which is exactly what you
want.
--
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 Sep 17, 5:48 pm, nospam wrote:
Hello,

We've got a gravity fed CH system. I think you call it plan C. I don't
know everything because much of it is hidden under the floor or behind
boxes but it seems as though we have 28mm pipe from the boiler to the
cyclinder. There is only one pump (next to the boiler) and no valves.
The pump is energised by the room thermostat for the CH. There is no
cylinder stat.

So it's not totally gravity fed, the CH is pumnped, only the HW is
gravity fed.

My father's old system was completely gravity fed and the gas boiler
did not use electricity (clockwork clock). It might not have been
very efficient but it worked during power cuts!

Robert