Any CH Wiring experts!

[Pete]

Any CH wiring experts out there!

Current heating wiring was put in by someone who practiced creative wiring - hence no wiring centre

System is semi gravity

There is a switched live on the programmer./thermo stat for CH ON or HW ON. Output goes live when heat called for. There are output for live when off (ie. spdt) but these are currently not connected.

When HW ON - there is power to Swl L in the boiler and the boiler fires up.

When CH ON - there is power to L in the boiler and the pump runs (no boiler) and Swl L is off. Pump is connected to the boiler

When HW & CH is on, the pump runs and the boiler is fired. (i.e we get central heating and HW)

We therefore have the following situation:

Both CH & HW On we get Hot Water and Heating - i.e OK If HW Only is on: We get Hot Water - No Heating i.e OK If only CH Only is on: We get Pump Only i.e Problem

I cannot wire the CH On output to Swl as it would work backwards - i.e HW On we would then get pump.

How can this be rewired to give CH Only. I reaslise that there is currently no valve on the system, so HW temp control is only provided when in HW only mode. If CH is running then there is no control of HW temp.

How should a valve be wired in to given addtional control?

[Christian McArdle]

There is usually a zone valve with an additional switch that fires up the boiler in parallel with the hot water system.

Alternatively, a relay may be used.

This depends on your boiler. Some boilers require an open loop through the hot water cylinder to dump heat. Some require careful routing of pipework to ensure emergency venting and quenching water supply. Some don't care at all, enabling you to place zone valves on the hot water circuit. What is possible depends on the boiler design.

Christian.

[Set Square]

With a conventional semi-gravity system, you *cannot* have CH only - because when the boiler is on for the CH, it automatically heats the hot water too! The HW switch controls the boiler amd the CH switch controls the pump - usually via a room stat - but the boiler has to be forced on for CH to work. Many programmers have an internal link which needs to be left in place on such systems - which effectively turns HW on whenever CH is turned on.

If your gravity HW system heats the water fast enough, your best solution - rather than going fully pumped - is to convert it to a C-Plan. [See

]

For this you will need a 2-port zone valve and a tank stat on the hot water cylinder (if you don't already have one). This gives truly independent control over CH and HW, and also provides a boiler interlock so that the boiler only fires when either or both circuits require heat - and shuts down when both demands are satisfied (i.e. when both stats are open) thus saving fuel.

[Pete]

Looks like order a "2 port valve then"

An I right in thinking that to wire I need to:

Connect thermostat HW On to: Valve Brown Permanent Live to: Valve Grey thermostat CH On: Valve White and Pump L

Boiler L to Valve Orange

plus neutral & earth

Thus, boiler gets power when valve activated (via grey) Boiler gets power when valve off (via valve white)

Currently the boiler has a connection for the pump. I assume that this should be left so that the pump can continue to run when the tank theremostat is cycling.

[Christian McArdle]

Before designing the system you need to determine

(a) Will your boiler be safe with a valve on the hot water circuit. Some older boilers (and most more recent solid fuel ones) will not be safe.

(b) Will the planned circuit still be safe in terms of boiler venting and water supply? If not, is an alternative pipe routing possible?

Christian.

[Pete]

Checked boiler manual and it shows an "optional" zone valve on the CH circuit. Boiler is not too old (potterton profile)

Valve would not affect venting/feed.

In additional there is an overheat thermostat on the boiler.

[Christian McArdle]

Sounds good. You can consider a valveless double pump system as well, if you prefer. It was done recently, although I can't remember the thread title. It involved various ingeneous ways of reducing the number of relays required...

Christian.

[Set Square]

The wire colours may vary, but if you study the Honeywell wiring diagram referenced earlier, and wire it *functionally* the same way, you should ok.

As Christian has said, make sure that the boiler doesn't mind zone valves - and that you install the valve in a position which doesn't interfere with the un-interrupted vent and fill functions. A good place is in the HW flow pipe very close to the hot cylinder *after* the point where the vent pipe connects.

I'm a bit puzzled by your reference to a pump connection on the boiler. This normally only applies to fully pumped systems, and keeps the pump running for a bit after the boiler has stopped firing in order to stop the residual heat in the boiler's metalwork from causing it to overheat. With a gravity system, the boiler needs to be able to take care of itself in HW-only mode - where the pump doesn't run at all. Are you *sure* it is a gravity system? If so, please clarify how the pump is currently connected and what, if anything, the boiler's pump connection is used for.

[Pete]

Just come down from the loft. It is definatly a gravity system.

The boiler is fully pumped/gravity switchable which may account for the pump outputs in the boiler wiring.

After a bit of a playaround, as far as I can see if power is put to the Swl input - just the boiler fires up (i.e we get HW only)

If power is provided to the "L" input then just the pump runs

If power is provided to "L" input AND "Swl" input then boiler and pump run (i.e we get heating AND water)

As far as I can see the pump is wired directly to the boiler pump output - with no other connections.

[Set Square]

How does looking in the loft prove that it's a gravity system? I wonder whether we mean the same thing by "gravity system".

I am talking about gravity (or natural convection) circulation within the

*primary* hot water circuit. If this is what you have, you will probably have *four* water pipes connected to your boiler - 2 large (28mm) ones which go to the indirect coil in the hot water cylinder, and two smaller ones (22mm) for the central heating - with the pump being somewhere in that smaller circuit - and with the primary flow in the HW circuit being *unpumped*. Is that what you've got? [I wonder whether you're defining "gravity system" in terms of having a large header tank for the hot water system - so that hot water flows by gravity (rather than by mains pressure) to the hot taps. If this is the case, we could be at cross-purposes, and may need to start again!]

[Pete]

99.9% sure. HW circuit is not pumped, only central heating - see below.

Not quite. I have TWO 28mm pipes going to the boiler. These 28mm pipes form the HW flow and return.

From the 28mm flow there is a T piece and a 22mm pipe connecting to the pump and then continuing to the CH flow.

CH return connects from a 22mm pipe to the 28mm Return via a T.

Is this still what you mean by gravity. - Would a diagram help?

[Set Square]

I can picture it from your description without requiring a diagram.

It certainly sounds as if you have a gravity HW and pumped CH system - with two independent circuits which share a bit of pipe close to the boiler rather than being separately connected to the boiler.

If you go for a C-plan system, connect the pump as per the C-plan circuit diagram rather than leaving it connected to the boiler.

[Christian McArdle]

I'd convert to S-Plan fully pumped, myself. Sounds like a fairly simple job. It might even be possible to go sealed pressurised at the same time.

Christian.

[Pete]

Right - new problem (but I think I know the solution)

Just got the 2 port valve, and when having a look at the wire noticed that the white didnt have an inner core (just a the plastic covering).

After checking the lid of the valve the diagram shows there is a microswitch which just connects grey and orange when the valve is open, thus we can fire the boiler when the HW is ON.

Am I right in thinking that this valve cannot be used without the NC link to the pump heating?

After opening up the valve, I note that the "dummy" white cable is cut short. I then consider swapping the relay for a SPDT, and after looking find that one is already fitted but not wired? (why???)

I cannot connect the white wire as it is a dummy! so will need to replace the 1m or so of flex to make a connection to the white.

[Set Square]

If you're converting to a C-plan, the switch on the zone valve - which operates when the valve opens - *needs* to be a changeover switch with NO, NC and COM - otherwise it won't work. If your valve isn't like this, swap it for one which *is*.

If, on the other hand, you're aiming at a fully-pumped S-plan system, with

*two* zone valves, the switches on those only need to be of the simple on/off type.

[Set Square]

[Apologies for not trimming the earlier reply - thought I had! The question and answer *should* have looked like this, will all the previous stuff removed].

If you're converting to a C-plan, the switch on the zone valve - which operates when the valve opens - needs to be a changeover switch with NO, NC and COM - otherwise it won't work. If your valve isn't like this, swap it for one which is.

If, on the other hand, you're aiming at a fully-pumped S-plan system, with two zone valves, the switches on those only need to be of the simple on/off type.

[Phil Nettleton]

take a look at the grunfos pump plan its a twin pump valve assembly see if this will do the trick