Rewiring unorthodox S plan to a standard setup (central heating & Hot water)

Hello there,

I’m in the process of mapping out a relatively standard S-plan system for my parents central heating and hot water system. Not sure exactly who set this all up in it’s current layout however it is certainly non-standard in several ways and is very inefficient and expensive to run. I believe the main reasons for it having been setup this way is the fact that we have both missing components and incorrect component types used – allow me to explain:

Firstly there is no room thermostat.

Secondly there is only a single channel programmer where there should be a dual channel one – the programmer is currently only talking to the Central heating (CH) valve.

The hot water (HW) override or ON button is currently activated by turning the dial on the boiler from 0 to a value from 1-5. (see figure 2 at bottom of post)

The dial also needs to be toggled for the CH to work – therefore if you ever need CH then you also heat the HW (even if you don’t need it!).

I have purchased a new dual channel programmer (drayton LP722) and also a wireless thermostat (un-wired control panel that can sit anywhere in the house & a receiver that will wire into the S-plan)

I have gone ahead and created a wiring plan of the existing system – please see figure 1 below (see figure 6 at the bottom of the thread for a photo of the below board):

FIGURE 1

I've been using this youtube guide https://www.youtube.com/watch?v=V9rN5D-wQIc&list=PLSZxXA-RQriDrN__RSLdadhjneMBDrNwL&index=52 and a couple of others as primary reference point for what I actually need to get to in the end - I intend on creating another diagram as above with the intended layout once I have cleared a couple of points up.

These are a few notes and questions I jotted down as I went (the key questions are marked in red):

1.1 - Currently the black wire from the BOILER (L or PL – Pump Live) connects to the reddish brown wire from the HW 2w Valve via junction 3.

1.2 - In the new setup – does the black wire from the BOILER (L or PL – Pump Live) need to connect to the PUMP L brown wire – therefore move the pump brown from junction 1 to junction 3?

1.25 - (Or do we just leave the PUMP brown on SwL terminal 1 and terminate the Boiler black wire? (with a rubber cap or isolate it on it's own terminal)

My first question is generally with regards to the above points 1.1, 1.2 & 1.25:
The pump is not directly wired into the boiler - the wire from the pump just connects to the junction board with the brown (live wire) connecting to the same junction section as both valves and the SwL from the boiler.

As the notes above suggest, I'm not sure what to do with that black wire. In the youtube guides I have watched there is only the L wire that comes out and talks to other components, however I have this extra black wire which is currently connected to the HW valve - (see figure 1 for what it currently is)(see below figure 5 for what I have been using as reference for what I need to reproduce in the new setup) .

FIGURE 5 (screen capture from youtube)


I also attached figure 4 at the bottom of the post for a photo reference of the wiring harness inside the boiler which is marked with pump where the black wire comes from.

2.0 - The HW 2wV reddish brown wire needs to connect to the HW thermostat brown wire. Move the Reddish brown wire to junction 4 to make this connection. (currently the HW thermostat L is on it's own therefore the thermostat must not be working at all at the moment? It needs to talk to the HW 2wV)

3.0 – Programmer wiring – currently L and 1 are linked with a brown cable bridge: this may or may not be needed for the new setup? Look into this.

So the question here is do I need to maintain that bridge between L & 1 on the programmer? - the new dual channel programmer is a drayton LP722 and it's instructions show the following (figure 3) which would suggest that it is needed. However the guides I have been watching on YT have made no reference to bridging the L & 1 terminals.

FIGURE 3



Any assistance or clarity that can be offered would be much appreciated, please let me know if any further explanation or photos are needed.

Thanks

FIGURE 2 - dial on boiler currently used as on/off switch for HW but also needs to be turned on for CH override too

FIGURE 4 - harness inside boiler (section with black wire marked as 'Pump')


Figure 6 - current junction box board.

Looks like you're using John Ward (flameport.com) resources, they are handy that's for sure.

You may find it more productive to ask this question on our sister site (plumbersforums.net), it could be a simple electrical fix but any layout changes are best done by a plumber, they can also deal with any gas side of it too whereas us mere sparks can't

In your diagram, and as you describe, the HW 2-way valve brown (feed) goes to your terminal 3, but the cylinder thermostat (brown?) wire goes to terminal 4. They should normally be connected together as the cylinder stat is supposed to be providing the power to the 2-way valve (as per John Ward's diagram).
It seems it might have been wired incorrectly as the HW valve is powered by the pump overrun output, so when activated it feeds the switched live from the boiler back to the pump overrun output of the boiler!

Unless the system needs pump overrun I would leave the pump connected to boiler switched live, and not use the pump L terminal on the boiler.

Regarding your query on the bridging link on the programmer - the contacts are often provided "volt free" and you need to provide mains power to the relay common contacts if you are taking power off to a load. It looks like the Draton Simp-L-fit wall mount/base provides those links for you, but if you have a programmer without that part you will need a link. John Ward's diagram assumes L is connected in the programmer to the relay common contacts.

In summary:
1.2 You can but you need to take the HW valve brown out of 3
1.25 Yes
2.0 Yes

PS the wiring centre looks a bit chaotic, and there should be cable clamps restraining each flex. Might be safer to replace it, or get that done professionally.

Are you sure your HW is pumped to the cylinder, and not just relying on old style thermo syphon? The boiler has a red switch beside the dial which is set to 'gravity' rather than 'fully pumped'.

brianmoooore said:

Are you sure your HW is pumped to the cylinder, and not just relying on old style thermo syphon? The boiler has a red switch beside the dial which is set to 'gravity' rather than 'fully pumped'.

Click to expand...

Or is the reverse "C" shape you can see in the lower half of the red plastic, the pokey-out toggle of the slide switch?
I have no idea!

Lister1987 said:

Looks like you're using John Ward (flameport.com) resources, they are handy that's for sure.

Click to expand...

Yeah I watched his entire series on the topic actually, his simple step by step, no nonsense break downs are excellent.
okay great - well If I can't get to the bottom of things on here I'll certainly head on over to plumbersforums for more trouble shooting however it looks as though I've already had some informative feedback in the responses which is great!

Avo Mk8 said:

In your diagram, and as you describe, the HW 2-way valve brown (feed) goes to your terminal 3, but the cylinder thermostat (brown?) wire goes to terminal 4. They should normally be connected together as the cylinder stat is supposed to be providing the power to the 2-way valve (as per John Ward's diagram).
It seems it might have been wired incorrectly as the HW valve is powered by the pump overrun output, so when activated it feeds the switched live from the boiler back to the pump overrun output of the boiler!

Unless the system needs pump overrun I would leave the pump connected to boiler switched live, and not use the pump L terminal on the boiler.

Click to expand...

Yep, will be connecting the cylinder thermostat to the valve.

Right, gotcha - that's what I was thinking, I'll probably go that route and isolate the black boiler live.

Avo Mk8 said:

Regarding your query on the bridging link on the programmer - the contacts are often provided "volt free" and you need to provide mains power to the relay common contacts if you are taking power off to a load. It looks like the Draton Simp-L-fit wall mount/base provides those links for you, but if you have a programmer without that part you will need a link. John Ward's diagram assumes L is connected in the programmer to the relay common contacts.

Click to expand...

I don't have the Simp-L-fit, just the basic universal back plate. So possibly I will need to maintain the L>1 bridge which is currently in there. However - strangely position 1 is not even utilized because it's single channel at the moment using position 3 for CH communication. Therefore is that bridge between L>1 even doing anything? there does not seem to be a link between 3 and 1 so is voltage even getting to 3 ?

Avo Mk8 said:

PS the wiring centre looks a bit chaotic, and there should be cable clamps restraining each flex. Might be safer to replace it, or get that done professionally.

Click to expand...

So there is actually a clamp at the bottom usually, however I removed it so I could move the wire bunches around for photos, i'll be putting the retention clamp back on for sure. I'll also be be adding crimped connectors to the terminals as currently it's just bare twisted wire which can crumble in my xp.

brianmoooore said:

Are you sure your HW is pumped to the cylinder, and not just relying on old style thermo syphon? The boiler has a red switch beside the dial which is set to 'gravity' rather than 'fully pumped'.

Click to expand...

Avo Mk8 said:

Or is the reverse "C" shape you can see in the lower half of the red plastic, the pokey-out toggle of the slide switch?
I have no idea!

Click to expand...

Right so it is actually set to pump - that C shape groove position denotes the ON setting. As to your question, I'm fairly sure it does use the pump. see below:

Therefore is that bridge between L>1 even doing anything? there does not seem to be a link between 3 and 1 so is voltage even getting to 3 ?

You are correct, assuming the single channel programmer that's there has connections as per John Ward's video!
It probably does - do you know the brand and model number of the programmer just to check.
If, for example, it was Hive single channel receiver, that requires a link between L and 1 because 1 is the common relay contact on that device! (thermostat convention rather than programmer convention?) Probably what I was thinking when I wrote wot I wrote earlier

Some interesting plumbing there! If your flow direction is correct, the connections to the cylinder are the wrong way around.

Avo Mk8 said:

Therefore is that bridge between L>1 even doing anything? there does not seem to be a link between 3 and 1 so is voltage even getting to 3 ?

You are correct, assuming the single channel programmer that's there has connections as per John Ward's video!
It probably does - do you know the brand and model number of the programmer just to check.
If, for example, it was Hive single channel receiver, that requires a link between L and 1 because 1 is the common relay contact on that device! (thermostat convention rather than programmer convention?) Probably what I was thinking when I wrote wot I wrote earlier

Click to expand...

The existing programmer is a 'Drayton Tempus one' and according to the manual "Tempus 1 has volt-free switching so a link from L to 1 is required MAKE SURE MAINS INPUT HAS for 230V output"

brianmoooore said:

Some interesting plumbing there! If your flow direction is correct, the connections to the cylinder are the wrong way around.

Click to expand...

Well you've made me doubt myself now - but I assume that direction is correct with the water coming down from the tank in the loft and entering the pump as per the arrows I drew in that photo. The plumbing is as it was when we moved here in 2002, so thankfully we can't take responsibility for that if there is indeed a mistake in the setup - either way being a loop I suppose in or out the water gets warmed either way.. perhaps less efficiently though.

zarrin said:

The existing programmer is a 'Drayton Tempus one' and according to the manual "Tempus 1 has volt-free switching so a link from L to 1 is required MAKE SURE MAINS INPUT HAS for 230V output"

Click to expand...

Thank you for coming back with the clarification. It seems the link is needed for the present programmer, but you won't need it for your Drayton 2 channel replacement.

Regarding the direction of flow, I suspect you have drawn what is happening, even if unconventional! I think there is an arrow on the side of the brass casting of each Honeywell valve, indicating the intended direction of flow. If you can see that it might confirm your supposition!

There's an arrow cast into the pump body which shows direction of flow. It's also fairly obvious from the back of the pump - you can see by the shape of the casting how the inlet port feeds to the centre of the rotor.
If the flow direction marked on your diagram is wrong, then the flow through the cylinder is correct, but the valves will then be on the inlet side of the pump, which puts them under negative pressure, raising the possibility that air will be drawn in through the spindle seal with the ensuing corrosion problems.