I have just installed a C27 controller to my system, which consists of a boiler, pump, tank stat and room stat. I have wired as best I can to wiring diagram. The diagram shows a link between the 2 stats but I have no wires left. Does any one know if I should fit a bridging wire and if so where.

The system is gravity fed.

At present the stat on the tank starts and stops the boiler, and the room one activates the pump only.

The controller I had previously started the boiler from the room stat.

very confused.

anyone got a photo of the wiring of the same controller?

Thanks
Ian

In an earlier contribution to this discussion,
IanJones wrote:

I have just installed a C27 controller to my system, which consists
of a boiler, pump, tank stat and room stat. I have wired as best I
can to wiring diagram. The diagram shows a link between the 2 stats
but I have no wires left. Does any one know if I should fit a
bridging wire and if so where.

The system is gravity fed.

At present the stat on the tank starts and stops the boiler, and the
room one activates the pump only.

The controller I had previously started the boiler from the room stat.

very confused.

anyone got a photo of the wiring of the same controller?

Thanks
Ian

Do you have a motorised valve in your gravity HW circuit? If so, you have a
C-Plan system. Have a look at the C-Plan wiring diagram in
http://content.honeywell.com/uk/homes/systems.htm
Pay particular attention to the wiring of the secondary contacts in the
valve (orange, grey and white wires). It is essential that you get this bit
right.

If you *don't* have a motorised valve, I don't see what function is served
by having tank stat - and, in any case, you would probably need an
additional relay somewhere to be able to make use of it.

Essentially, when HW only is calling for heat, you need to run just the
boiler, and turn it off when the demand is satisfied. When CH is required,
you need to run both the boiler *and* the pump. In this condition - unless
you have a valve in the HW circuit, the HW will continue to get hotter -
even when it's above its stat setting.

Perhaps you can provide a few more details about your physical system.

--
Cheers,
Set Square
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On Mon, 26 Sep 2005 19:09:46 +0100, Set Square wrote:

The diagram shows a link between the 2 stats but I have no wires
left. Does any one know if I should fit a bridging wire and if so
where.

You need to bring the "HW satisfied" aka HW HOT contact from the tank
stat to the CH stat somewhere but I forget where, it is very confusing
but logical when you follow it through. Works the logic and produces
this, I think it's correct (ASCII art fixed pitch font required...)


Tank Stat
HW ON ---------o Cold
Comon o----------------- BOILER
+---o Hot
|
+-------------+
Room Stat |
Cold o--+-------------- PUMP
CH ON ---------o Common
Hot o-- no connection

Live wiring only, earths and neutrals ommited for clarity.

If you *don't* have a motorised valve, I don't see what function is
served by having tank stat...
snip
Essentially, when HW only is calling for heat, you need to run just
the boiler, and turn it off when the demand is satisfied.

You answer you own question, thats what the tank stat does. B-)

When CH is required, you need to run both the boiler *and* the pump.
In this condition - unless you have a valve in the HW circuit, the
HW will continue to get hotter - even when it's above its stat
setting.

This is true but is the way a lot of older systems are installed.

--
Cheers
Dave. pam is missing e-mail

If you visit the screwfix web site and enter 94777 in the quote number,
it brings up the Horstman control pack that features this controller.
If you download the pdf instruction manual below the main image this
gives the wiring for various systems (2 or 3 port valves, pumped or
vented systems etc)

I just installed one of these kits (purchased 9 months ago !) and it was
simple to follow with the existing cables. It also shows you how to add
links if you omit any room stat etc.

Malcolm



Dave Liquorice wrote:
On Mon, 26 Sep 2005 19:09:46 +0100, Set Square wrote:


The diagram shows a link between the 2 stats but I have no wires
left. Does any one know if I should fit a bridging wire and if so
where.


You need to bring the "HW satisfied" aka HW HOT contact from the tank
stat to the CH stat somewhere but I forget where, it is very confusing
but logical when you follow it through. Works the logic and produces
this, I think it's correct (ASCII art fixed pitch font required...)


Tank Stat
HW ON ---------o Cold
Comon o----------------- BOILER
+---o Hot
|
+-------------+
Room Stat |
Cold o--+-------------- PUMP
CH ON ---------o Common
Hot o-- no connection

Live wiring only, earths and neutrals ommited for clarity.


If you *don't* have a motorised valve, I don't see what function is
served by having tank stat...

snip

Essentially, when HW only is calling for heat, you need to run just
the boiler, and turn it off when the demand is satisfied.


You answer you own question, thats what the tank stat does. B-)


When CH is required, you need to run both the boiler *and* the pump.
In this condition - unless you have a valve in the HW circuit, the
HW will continue to get hotter - even when it's above its stat
setting.


This is true but is the way a lot of older systems are installed.

There does not appear to be a motorised valve.

So are you suggesting that I omit the connection to the tank stat and connect the boiler direct to the controller?

If I do this it means that the tank temp is not being taken into consideration so the water in the tank could exceed required hot water temp, or will it stay at temp set on room stat?

Thanks
Ian

On Wed, 28 Sep 2005 15:33:37 +0100, IanJones wrote:

There does not appear to be a motorised valve.

So are you suggesting that I omit the connection to the tank stat
and connect the boiler direct to the controller?

I'm not, I'm not sure about Set Square... B-)

Have you not seen my previous post?

If I do this it means that the tank temp is not being taken into
consideration so the water in the tank could exceed required hot
water temp, or will it stay at temp set on room stat?

Without a tank stat the hot water will always rise towards the
temperature of the primary water, as set by boiler stat, probably
around 80C ouch.

It will still do this with a tank stat when the heating is also
calling for heat. When the heating isn't calling for heat the tank
stat will shut the system down when it is satisfied.

--
Cheers
Dave. pam is missing e-mail

In an earlier contribution to this discussion,
Dave Liquorice wrote:

On Wed, 28 Sep 2005 15:33:37 +0100, IanJones wrote:

There does not appear to be a motorised valve.

So are you suggesting that I omit the connection to the tank stat
and connect the boiler direct to the controller?

I'm not, I'm not sure about Set Square... B-)

OK - I've just drawn a circuit diagram on the back of an envelope which I
*think* will work.

Tank stat must be the changeover type - with common (COM), nornally open
(NO) and normally closed (NC) contacts. The room stat can be a simple on/off
device.

Make the following connections:
Programmer HW output to tank stat NC
Tank stat COM to boiler switched live (SL)
Programmer CH output to room stat input
Room stat output to pump *and* (this is the clever bit!) to tank stat NO

So the boiler will run whenever there is either (or both) a HW or CH demand
and the pump will run whenever there is a CH demand.

The only problem is that the boiler will run when there is a CH demand
*even* if the HW demand is satisfied - so the HW will get *too* hot. The
simplest way to fix this is to install a zone valve in the HW circuit and
convert it to a C-Plan system.
--
Cheers,
Set Square
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Please reply to newsgroup. Reply address is invalid.

The simplest way (can't be bothered to troll through all the posts) is
to install a three way valve, room stat and tank stat. This way you can
set different timings for the HW and CH and both can be switched so you
have one, t'other or both on at the same time. - also does your boiler
have pump over-run ?

If you get stuck, drop me an e-mail and I'll take some photo's of the
wiring as I've just installed a Horstman instalation kit - it might help ?

Malcolm

Set Square wrote:
In an earlier contribution to this discussion,
Dave Liquorice wrote:


On Wed, 28 Sep 2005 15:33:37 +0100, IanJones wrote:


There does not appear to be a motorised valve.

So are you suggesting that I omit the connection to the tank stat
and connect the boiler direct to the controller?

I'm not, I'm not sure about Set Square... B-)


OK - I've just drawn a circuit diagram on the back of an envelope which I
*think* will work.

Tank stat must be the changeover type - with common (COM), nornally open
(NO) and normally closed (NC) contacts. The room stat can be a simple on/off
device.

Make the following connections:
Programmer HW output to tank stat NC
Tank stat COM to boiler switched live (SL)
Programmer CH output to room stat input
Room stat output to pump *and* (this is the clever bit!) to tank stat NO

So the boiler will run whenever there is either (or both) a HW or CH demand
and the pump will run whenever there is a CH demand.

The only problem is that the boiler will run when there is a CH demand
*even* if the HW demand is satisfied - so the HW will get *too* hot. The
simplest way to fix this is to install a zone valve in the HW circuit and
convert it to a C-Plan system.

On Wed, 28 Sep 2005 23:21:55 +0100, Set Square wrote:

OK - I've just drawn a circuit diagram on the back of an envelope
which I *think* will work.

You describe what I drew in my other post...

The only problem is that the boiler will run when there is a CH
demand *even* if the HW demand is satisfied - so the HW will get
*too* hot.

Correct.

The simplest way to fix this is to install a zone valve in the HW
circuit and convert it to a C-Plan system.

Not forgetting to make provision for any pump overrun if the boiler
requires it. This being an old and gravity system the boiler probably
doesn't need it but worth checking.

--
Cheers
Dave. pam is missing e-mail